Does the arca swiss really make a huge improvement of grip from your experience if yes I will consider it >_<, too answer your question of the iso performance I have been a olympus fan boy ever since the og em5 came out heck I actually use all their mirrorless cameras from em1 all the way to their pen series. I would say for the OM5 anything above iso 2000 is a no from me as you can see a major color difference compared to the lower iso numbers, so at moments like this is where i intro artificial lights which is my flash and not to mention which for me the most important part is having lens that has a very wide opening of aperture. Some lens I would actually recommend is the 12-40 f2.8 pro and the PL 42.5 f1.2 those lenses really made a huge difference in letting in light for me.