In MF you won't find much if anything faster than f/2,8 and the difference in DOF from f/2,8 to f/3,5 would I say is minor.
DOF in a MF neg seems, to me at least, to be shallow at those appertures.
Which focal lenght are you looking for in 35mm RF glass? Mind you that fast teles (75< ) are more difficult to focus than similar SLR lenses, the RF base on the Bessa may be just to short for that task unless you use e.g. a nikon 2X magnifier. If you want to stick with normal lenses maybe a Canon QL 17 GIII would fit the bill and a TLR with a f/2,8 lens could be a MF option.