[thxbb12]

Why not?

And as being equivalent to a 24-80mm f5.6, in what way is it more versatile to a 24-70mm f4 on FF (or 24-80mm f5.6 on FF, if such a thing would exist), a 17-55mm f2.8 on APS-C?

That is the same thing as saying with f5.6 and a usable ISO <setting> of 12800 on the D600/6D cameras... 

It is a nice lens on the platform, as I said. But not so nice when you look cross platform. Anyway, I am pretty sure that at 16mp on the MFT sensor, you will already have loss of resolution due to diffraction at f5.6. Just like you have loss of resolution due to diffraction on FF at f11 (and on APS-C at f8).

As I said, nice lens on MFT. But it is not a lot smaller than "f4" lenses on APS-C, is it?

 

By looking at the SNR graph for both the EP-5 and the D600 at dxomark.com, it appears there isn't 2 stops of difference in terms of noise between the 2 sensors. It looks more like a 1 1/3 stops of difference. Therefore, ISO 3200 on the EP-5 should offer similar noise performance to ISO ~8000 on Nikon FF. In theory it should be 2 stops, but in practice there is some efficiency loss it seems. And all of this is not including the benefit of Oly's incredible IS system.

 

The thing is, MFT has easily reached "good enough" IQ for me (using latest sensors), even at high ISO (up to 3200). Mind you, I own a D800 and I don't use it much since I bought into the MFT system very recently.  Most of the time, I don't want to lug my D800 kit around, so instead I grab my Pana G3 + 14 f2.5, 25 f1.4 and 45 f1.8. Despite that sensor being outdated compared to the one in the OM-D, I still grab my G3 in place of my D800! The G3 + 14mm fits in my short's pocket, that's soooo convenient! I never thought I would favor my MFT gear over my FF kit. Well... it happened.

Originally, I had bought the MFT kit for occasional snapshot on my way to work. Funny how things turn out.  My dad has an E-PL5 and the IQ is really good for 95% of my needs... I think we have reached very high IQ standards and it's very very difficult to distinguish between cameras' output regardless of the format, except perhaps under exceptionally challenging conditions.

What I forgot to mention is AF inaccuracy: this is also one of the main reasons I'll never consider going back to traditional mirror DSLRs. I find it so liberating to know my photo is gonna be sharp and the focus will be exactly were I wanted, regardless of the lens or the lighting conditions.

 

From my point of view (I'm no pro), carrying a big backpack full of FF lenses doesn't justify the IQ difference over the convenience MFT provides. In the real world, as long as I don't print a 3 by 2 meter billboard, I find the difference in IQ between FF and MFT to be insignificant. Of course, your mileage may vary. 

 

Oh and I now enjoy photography much more than before