Yes, I've heard of SU-85 tactics being successful. Are you pumping out SU85 only or SU 76 as well. And how good SU76 is? Does it have same stats as ZiS-3?
I never build SU76s. It's a waste of fuel, imo, it just delays you getting an SU-85 out faster. If there some barrages needing to be done--mortars and ZiS-3, but the barrage abiltiy on the ZiS is expensive.