[tilky]

As far as the processor is concerned, the difference is minimal, it even exists at all. Surely with the current code it would not make a difference. My suggestion would be to stick with the 4 pwms. If I remember correctly our team had a pwm come out at a competition. But since we had another one on that side, we could still drive. Granted it was slower and we had to adjust steering, but at least we didn't just sit on the field.
I would say only to go with the y-pwm if you ran out of pwm for other motors (highly unlikely)