For me m4/3 is a good compromise between features and performance. The lenses are sharp and small. Larger aperture lenses are going to be expensive and larger. A full range of 1.7/1.8 lenses are great. But I'd be lying if I said that there isn't a difference in stills. For me I use zooms exclusively outdoors and indoors and in low light I'm using primes. On my FF cameras I would use my 2.8 zooms indoors since higher ISO performance was stronger. 2.8 on a m4/3 and 2.8 on a FF will behave differently, not just in terms of DoF but in terms of acceptable noise. On FF my preferred ceiling was 6400, sometimes venturing to 8000-10000 on the newer cameras. I do find it true that FF is about two stops better than m4/3 in terms of noise, so for me my preferred ceiling is 1600, going up to 3200 rarely and higher even fewer if I just want to get the shot. But luckily the GH5 has a pretty good IBIS system and when combined with lens IS, the Dual IS system works very well. So if my subject isn't moving then I'll be able to shoot at 1/25 or slower and still get the shot.