TriX Loc: Raleigh, NC

The 5D4 the OP mentioned has the same resolution as the R7. Not sure what you mean by better ISO, but the 5D4 has identical DR and a full stop better low light/high ISO performance. The R7 does have IBIS, but both the 100-400 and the 24-105 have IS, and one would assume that a sizable percentage of shooting in Africa would be animals, where a high shutter speed plus IS on the lenses negates the advantage of IBIS. It would help in shooting landscapes handheld in low light, but remember the high ISO low light advantage of the 5D4.

The R7 is certainly an improvement over the 7D2 in many respects, but the statement that MILC (and the R7 in particular) produce better IQ than a DSLR such as the 5D4, given the same lenses, is not accurate except in some specific corner cases (such as BIF for example) where the addition of more AF points and a later gen AF may provide an advantage.

imagemeister Loc: mid east Florida

I did say there would be isolated exceptions for people to argue about....especially for full frame vs APSC !

The Pixel pitch of the R7 is much smaller than the 5D - if that is what we want to talk about - .....that is what I really mean by MP - cropping power/sharpness - assuming that the lenses would hold up to this.

The mirror slap and mechanical shutter vibration of the 5D is another matter for contention also .....

imagextrordinair Loc: Halden, Norway

The 1DX MK3 has a full electronic shutter, eye detection in both auto and manual, Manual lens assist arrows and focus assistant edge detection.

Advanced and still superb. Has a mechanical shutter but I rarely use it...

TriX Loc: Raleigh, NC

But this is a case where the OP is considering carrying both the 5D4 and an R7, and except for the a hundred or so grams of weight (remember the R7 will need an adapter), the systems are very close in size and weight since they are using the same lenses, and I doubt seriously if shooting the same lens, you could tell any IQ difference, except that in low light, the 5D4 will produce less noise at the same ISO or the same noise at over twice the ISO or the R7. Remember there’s a price for those small pixels.

The R7 does have 2 advantages though that have nothing to do with mirrorless vs DSLR, a higher fps (if you’re a “spray and pray” sort of shooter) with moving animals and the “crop factor” for long range shooting. Which brings up the original question of the extender. It depends on which gen 100-400 and 1.4x extender the OP has. The MTF charts from Canon show a VERY small (5%) difference in IQ with later gen 100-400Ls used with the MKII or MKIIi converter. BUT, I’m not sure combining a crop body with the 100-400 plus the extender is a very useful combination. It’s going to be difficult to shoot handholding the 840mm equivalent FL, and it’s going to be f8 minimum which will drive you to high ISOs (which the R7 is not great at) when you combine it with the high SS you’ll need to stop the action and minimize camera shake (even with IBIS and IS). I think I’d save the extender for use with the FF 5D4 if you use it at all.

imagemeister Loc: mid east Florida

Using what you have and with the goal of best IQ in most situations, I recommend doing the R7 ONLY with the 100-400 and the 16-35 and NO extender - and, again, also the RX10m4 at least as a back-up.

CHG_CANON Loc: the Windy City

As usual, visual evidence trumps uninformed opinion. Here's a bunch of images with the 100-400L II extended with a viii 1.4x. Possibly, the crop factor and pixel resolution of the OP's cameras will offset the 40% increase from the 1.4 extender. Personally, I shoot the 100-400L without the extender, when I don't need it. But, I don't hesitate to use this tool when I do need to 'stretch' to an effective 560mm on a full-frame 22MP body.

The EF Extender 1.4III revisited

Longshadow Loc: Audubon, PA, United States

So, if a company were to make a new camera with a mirror it would be just as good because of the new technology available?

ergo, it's not the mirror missing...
It's the technology in the new cameras.
That happen to not have a mirror.

Rlti Loc: Medford, OR

After 7 trips to SA, I agree with Hip Coyote with one small addition. Be sure to keep your cell phone handy for the inevitable shot where 24mm is not wide enough.

imagemeister Loc: mid east Florida

Mostly - but not totally .....

burkphoto Loc: High Point, NC

Most of the reasons mirrorless interchangeable lens cameras are better have to do with making photography easier in specific situations.

At least a few of them have to do with IQ, though:

Newer lens designs are generally better than older ones. Higher megapixel cameras demand better optics. Those better optics, combined with newer technology in the cameras, produce better results. Part of the reason for better optics is the shorter flange to sensor distance, which makes designing wide angle lenses much easier. But that isn't the end of it.

Newer sensors get all the latest technology improvements. They have higher megapixel counts, and better processors. The AF and stabilization systems are better. And because the flange to sensor distance is shorter, adapters can put older SLR and dSLR lenses on mirrorless bodies. That can generally improve the results from older lenses because the sensors and processors in the newer cameras are better.

As manufacturers put all their engineering into the new cameras and lenses, it will be a no brainer to upgrade when your older bodies die. Old lenses work on new bodies, so long as there are adapters.

Whether ALL the features of your old lenses are preserved depends on the adapter and the camera. In some instances, old lenses will work mostly as intended, even on different brands. For instance, Canon EF lenses work just fine on Leica, Panasonic, and Sigma bodies when fitted with the Sigma MC-21 Canon EF to L-Mount adapter.

CHG_CANON Loc: the Windy City

Canon EOS technology was developed in 1987 for the needs back then, and for every day since. The EOS-R models fully support every Canon-branded EF / EF-S lens ever released, all +120 million now sold worldwide, with Canon's EF-RF adapter. Similar adapters put them onto EOS-M too.

When we talk about mirrorless being better, we're talking about the newest DIGIC processor chips, and IBIS technology, and the newest sensor designs, typically as extreme pixel resolutions, even an entirely new CR3 RAW format.

Canon photographers can have full confidence in their legacy EF / EF-S lenses on all these new mirrorless models, as they consider the RF / RF-S options that skip the adapter.

SuperflyTNT Loc: Manassas VA

You don’t shoot much wildlife do you?

SuperflyTNT Loc: Manassas VA

Interesting that you talk about IQ after you suggest a camera with less IQ. The RX10MIV would be ok for regular tourist snapshots, but if I’m going on a safari I’m taking my best gear.

Longshadow Loc: Audubon, PA, United States

Just wait until the next version of "new".
Then we can all learn why they're even better.

imagemeister Loc: mid east Florida

The RX10 has the highest image quality of anything I own - @ ISO 400 or less ......I would definitely take it anywhere and enjoy the trip. It really is a PLEASURE to use the RX10. Yes, if I had $10 K invested in Z9 or A1 W/ lens, I guess I would take that and use the RX10 as back-up - but, I WOULD be taking the RX !

I would certainly take it over the OP's 7D II or 5DIV ! - the 5D being way too SLOW.

If you compare the RX to the Z9 or A1 or R3/5 or A7RV, the RX looses but IMO, for just about everything else, the RX competes at ISO 400 or less - for $1700 ! ! and 1/3 the size and weight....