Thanks for the replies. Been interesting reading the various opinions on the matter.
I decided to put the money down and get FMDrive. Might be my imagination, but I feel I can hear a difference between it and Genny/YM2612. As for Genny vs YM2612. Genny has a bigger UI, and that feels pretty much it. It seems much the same otherwise, aside from the PSG side of things.
I haven't messed around with FMDrive too much yet, just got it, so I'm not 100% sure about using it for drums. There's a ton of tfi's to go through, so there might be something there to work with, but there's so much and it's not really labeled outside of what game the instruments came from originally (though, considering the sheer bulk of it, I can understand that it's not feasible to label everything for what is, afaik, a one-man operation). Genny had some ok sounding drums in it, so for now I'll be using Genny for that and FMDrive for stuff like bass and guitars.