well Ive run 1/2, 1/4, 1/8, 1/16 all in hardware (r2r ladder) and all works well. I epoxied a NTC thermister into a heatsink that the mosfets are mounted to and under single stepping the heat sink never broke 40C. Im also using 1R 10w Rsenses for each phase but I think this is over kill. That and they are low tolerance cement types so just using 2 would be better.
The proto circuit seems to work fairly well so Im going to go ahead w/a pcb. Before I do I want create a scaling VDD supply for the uC since the r2r ladder is driven driver directly off the io ports, that way i can have true 8 bit resolution for 2.5a to 5A a phase.
Some blurry pics of the proto board and a single phase running 1/8.