My grip is that I can't get slow enough film - I generally use FP4+ or EFKE PL100. But you can now get PL25 - which I will try as soon as my current stock is reduced a bit.
So what's the problem? I usually have my camera on a tripod, some of the huge shutters go no faster than 1/50th, and I like to be able to chose the aperture for pictorial reasons. With ISO 400 film in sunshine, that works out to 1/50th at f:45 (from "sunny 16")!
That brings us far up into diffraction territory - and I really prefer to be able to open up to f:4.5... So I want slower film, not faster!