if you're talking HP gains with each head, the GSR head would come out on top....why?? because of the bumped compression you get with the GSR head....the difference in flow of the heads is so minor that it's not even a factor when dyno'ing each head against each other.

A minor P&P on the GSR head will solve any minor differences there are between the heads.

One thing to consider is the b16 head was meant for a 1.6L....a GSR head was meant for a 1.8L.