I believe he’s talking about the difference between the OM-1 and the just released OM-1 MkII. I never had a D7100 but I’ve had a D7000, D7200 and D500. All very good image quality, as is my OM-1, but when it comes to other capabilities the OM-1 completely blows them away. A lot depends on what you shoot, but I make good use of mine for all kinds of shooting. For wildlife there’s Pro Capture and 25fps with focus tracking, (50fps with the Pro lenses). For city night shooting I live Live ND and Live Composite. I’m not making the jump to the MkII because I just can’t justify the expense right now. It is tempting and if I didn’t already have the OM-1 I would get the new one. The biggest differences are a bigger buffer, improved AF, (although the autofocus was already very good), and for me, Live ND adding another stop to ND128.

Balderdash. The M4/3 weight/size advantage while it does exist…it's not as great as proponents of the smaller form factor expound on (I just checked on system weights today for an equivalent wildlife/landscape system). And there are tradeoffs because of the smaller sensor…and those tradeoffs may, or then again may not have any relevance to a particular user.

And claiming that the OM is the best weather sealing there is…where did you get that from? All of the competing models from other vendors have excellent weather sealing, just as the OM1 system does.

There are reasons that for some…M4/3 might be a better overall system…and then again there are reasons that DX or FX are also better or worse overall choices. Putting out grandiose claims like this just confuses the unwary.

While the 7100 is sort of dated technologically and sensor quality wise (i.e., newer sensors generally have less noise and a higher dynamic range)…there's nothing wrong with it and your current lenses from a quality point of view. I'm not an Olympus guy but the OM1's are mirrorless and it's really not fair to compare them with an older DSLR from an overall capabilities point of view. Because they're newer…like mirrorless from other brands…they have the EVF to go along with the newer generation sensor and the AF is considerably improved over older models due to ongoing tech change and Moore's Law.

What you need to do is decide for yourself whether the advantages that come along with mirrorless are worth investing in at this point in your photography life…and if so what budget you want to have…along with any physical limitations that might have an impact as micro four thirds bodies are smaller and their lenses are also somewhat smaller in general. You also need to take into account the whole OM works different and has different menus and button names and control names than Nikon…but then there's some learning curve even within Nikon going from the DSLR bodies and lenses to the mirrorless ones.

The weight advantage of the M4/3 systems is real…but in reality it's not as significant as some might claim…I checked earlier today and an OM 1 2 lens kit that has comparable focal length reach to a Nikon Z50 2 lens kit is less than a half pound lighter. The real weight savings of the M4/3 is that the crop factor is 2 so a 300mm lens is equivalent to a 600mm FF one…and a 300mm lens is lighter and smaller than a 600mm one is simply because of physics…but as I said comparing the weights it's relatively minor overall.

Personally if I was upgrading from a D7100 I would probably get a Nikon Z50 and depending on my needs would get some Z FX lenses because there's not a whole lot of choice in DX lenses in Z mount…but then there's a lot of muscle memory of where the controls are and how the menus are setup and while the Zs are different from the earlier DSLRs it's evolutionary rather than the revolutionary it would be going to any other brand.

What you'll get with any newer body and lenses than what you have now is all the advantages that come along with ever evolving tech…less noise, more MP, better dynamic range, better AF…as well as the advantages that come along with the shift from DSLR to mirrorless…the bodies are smaller because there's no need for the mirror box. A full frame Z5/6/7 series body is the same size and weight as the D7500 DX body that my Z7II replaced…and Z lenses are generally better, more controls, and also smaller and lighter than their F counterparts…again because of the wider Z mount throat, closer lens to sensor distance, and more sophisticated optical design software running on faster design computers.

If you stay in the Nikon family…then it's a choice between DX and FX and these days Nikon has pretty much identified their DX products as consumer models, not dedicated photographer models…largely because the DXs are designed to a price point that doesn't allow all the goodies the higher priced models have.

Balderdash. The M4/3 weight/size advantage while it does exist…it's not as great as proponents of the smaller form factor expound on (I just checked on system weights today for an equivalent wildlife/landscape system). And there are tradeoffs because of the smaller sensor…and those tradeoffs may, or then again may not have any relevance to a particular user.

And claiming that the OM is the best weather sealing there is…where did you get that from? All of the competing models from other vendors have excellent weather sealing, just as the OM1 system does.

There are reasons that for some…M4/3 might be a better overall system…and then again there are reasons that DX or FX are also better or worse overall choices. Putting out grandiose claims like this just confuses the unwary.