I have 5 for 3 years now. All have worked flawlessly. Even dropped one an it came apart but still works!
If you have one that is critical (HSS or the 560IV master). Buy 2 . All my speedlights added up equal the cost of 1 Canon branded light. If you need the extra speed of power recycle readiness at full power or "consistency of color" than pay the 6x cost. Id rather put my money in lenses and light modifiers...

Umm... FF cameras are low light / low noise head and shoulders above Crop cameras in general. As for cropping and printing...resolution has to do with pixels not whether its FF or crop. 1Dx which is a crazy expensive FF is only 18mp but you can get a $400 crop DSLR with 24mp.

...if you can afford FF and the associated avg doubling in prices for lenses...go for it. For indoor pictures in low light up to 3000ISO....its the difference between a great photo and something that looks like you took it off your smartphone. :-)

Took the exact shot last night from Toronto Canada. Looks identical in exposure too. 150-600mm SigmaC on a tripod with wireless shutter release. (Mine was cropped to get the framing you got. My guess is at 800mm, you had to crop yours a little also to get the photo you posted)

IV has significantly better DR, especially in the shadows (better on highlights too but not as big a difference). The AF is a big driver too but if you are in Museums...you probably dont need the superior AF in low light (you may have the patience to MF in low light in a museum). Your call. I have to say, if I had a 5diii and a 1DX, i would be having trouble justifying the 5DmkIV for your needs. Only would do it if I want to pull up the shadows in low light where the 5diii is mush, the IV will have detail.

Opteka lens with 2x convertor? Tripod used?
Would need to use mirror lockup and a 2sec timer or wireless shutter release at that range. I would not expect great sharpness with that lens combo but you might be able to squeeze a little better IQ tweaking your setup. What was the F stop and shutter speed?

They recommend you turn it off when mounting on a tripod.

Also if you are trying to shoot high shutter speed, fast moving objects that are far away...activating the IS as you focus while swinging the camera to track the object will cause the viewfinder to "jump around" as the IS tries to stabilize your camera....you are effectively fighting the IS at the moment and its hard to track the object through the viewfinder (only an issue with longer telephoto lense and not the 24-70)
Generally, IS is good for low light, motionless photos....amazing how low you can reduce the shutter speed and still get sharp photos.

I have the F4 IS and have used the 2.8. I dont think you will miss the IS unless you are photographing stills in low light....which for me is very rare.
All things being equal, I would take the 2.8 but happy with the F4 IS too...

6D -> Low light beast and fantastic pictures - terrible AF
80D -> all the bells and whistles (FPS, AF, DPAF etc etc) - IQ ? not even close to the 6D

2300 ISO on the 6D is about the same as 800 ISO on the 80D in equivalent noise...

If you shoot a lot of photos indoors/dimly lit and care about really high Image Quality - get the 6D
you want versatility (sports and stills) go 80D


Both are really good...however...if you want the BEST of BOTH - 5DMKIV :-)

ART line so far has exceptional quality optics. The 50mm and 85mm primes exceed all counterparts (even Zeiss in the case of the 50mm 1.4). CAVEAT! ... wait until its out to see the early AF reviews. 3rd party lenses do not have the benefit of AF algorithm collaboration. Nikon lens designers work with Nikon body designers to ensure optimum performance and future compatability with new body releases. Similarly Canon. The ART line of lenses are gorgeous however I have the 50mm1.4ART and went through 2 copies to get one that was acceptable. I would not trust it at small DOF (close to subject and sub f2.8) to get a 1 shot sharp image. Have resorted to taking mulitple shots or making manual adjustments. I use it for portrait/artistic shots but I use a native Canon lens for any shots with the slightest movement during a wedding or other "must have moments" that someone is paying for...Other Sigma lenses have had excellent AF results reported so its a bit hit and miss (I have the Sigma 150-600mmC and its AF is speedy and accurate - which is critical for Sports). One other note...its not about whether the focus misses...its whether it misses consistently. The 50mm1.4ART misses inconcsistently which makes Microcalibration useless. Wait till the new lens is out and do your research....

So.

...as another UHHer has said....patience grasshopper :-)

For emphasis :-)
...not sure how I did that...will be less emphatic next time...

Actually, my experience with VC on (IS on in Canon) will cause the image in viewfinder to "jump around" as you try to track a far away, fast moving object versus help "frame the image"....and at shutter speeds you are describing...VC does not add any value. When shooting at 600mm, VC will constantly try to stabilize and as you track...you will be fighting the VC system. Switch it off. I agree with everything else said...(and I could be wrong...perhaps VC is better than IS )

"Good" photos are based on your expectations.
Starting out, great photos with my kit kens....and then got into Lightroom and PS and started cropping, printing etc and noticed they werent perfectly sharp wide open...and now have FF cameras and pro lenses....incremental benefit for extreme cost :-) I do weddings part time and can justify the extra cost for the incremental benefit. I will say the "plastic fantastics" are awesome value. 35mm and 50mm 1.8 lenses for crop cameras. Would use them for anything except I replaced mine with a FF 50mm 1.4. Use the kit lens and buy a 1.8 so you can experiment with DOF artistry....then see if your spouse will let you blow the food budget on new lenses or a FF body when you are ready :-)

"Good" photos are based on your expectations.
Starting out, great photos with my kit kens....and then got into Lightroom and PS and started cropping, printing etc and noticed they werent perfectly sharp wide open...and now have FF cameras and pro lenses....incremental benefit for extreme cost :-) I do weddings part time and can justify the extra cost for the incremental benefit. I will say the "plastic fantastics" are awesome value. 35mm and 50mm 1.8 lenses for crop cameras. Would use them for anything except I replaced mine with a FF 50mm 1.4. Use the kit lens and buy a 1.8 so you can experiment with DOF artistry....then see if your spouse will let you blow the food budget on new lenses or a FF body when you are ready :-)

"Good" photos are based on your expectations.
Starting out, great photos with my kit kens....and then got into Lightroom and PS and started cropping, printing etc and noticed they werent perfectly sharp wide open...and now have FF cameras and pro lenses....incremental benefit for extreme cost :-) I do weddings part time and can justify the extra cost for the incremental benefit. I will say the "plastic fantastics" are awesome value. 35mm and 50mm 1.8 lenses for crop cameras. Would use them for anything except I replaced mine with a FF 50mm 1.4. Use the kit lens and buy a 1.8 so you can experiment with DOF artistry....then see if your spouse will let you blow the food budget on new lenses or a FF body when you are ready :-)

Re:bulbs being hidden. That is what I suspected. Need the point source to get starburst. Thanks to all who posted.