I tried a few options and made a decision to use hardware PWM. If you're in the same position that I was in > 12 months ago and need to drive servos and motors then by all means give software PWM a shot and please let us know what the results are like.

Also don't underestimate the complexity of the changes needed to fix the DMA library - there were several long threads about it. In fact browsing the repo now there may be signs of renewed activity - https://github.com/metachris/RPIO/issues