Eh...I was kinda looking for in all dimensions. My current build doesn't really have constraints, I just wanted to be efficient with the space the drive would take up.
I was originally trying to recreate an old redpower drive I found. Part of the issue was that I wasn't supporting some of the frame sliders. Also, I think that RP frame motors transferred their power, which FM frame manipulators don't.
Anyways, after experimenting a bit I found a 4x5x5 design I'm happy with.