Difference in comp between equity and non-equity partner at a mid-size PA firm?

There's a difference. It depends a bit on the nature of the nonequity role and if its considered temporary (2-5yrs) or could be a permanent position. Longer term nonequity partners normally would be compensated more in line with the value they bring to the firm, with some upside in a bonus plan if the individual exceeds targets. Some firms cap total comp for nonequity at a certain level, which is almost always lower than the average equity partner comp.