Fast Burn of ZZ-4 heads

Hello all. I'm new to the board and have a tech question for the head experts. The application is a stock ZZ-4 installed in a 24' sport cruiser. It uses a standard Mercruiser exhaust which is wet and quite restrictive and I don't want the noise of the thru transum. Has the larger Q-jet carb and a reasonable cold air intake system. The operating RPM range is 2700 to 5000 max. Currently the engine has a set of Fast Burns and perf is quite good. 4710 RPM and 44.1 MPH. Not bad for this heavy a boat. However, I have a set of new ZZ-3 heads...... same as ZZ-4 but with the orange springs. I am considering a swap. My thought is that the smaller valves and smaller intake runner will give beter velocity at the RPM range I run....... and thus a little more torque and perhaps a bit more HP at that RPM.
Any of you guys have any thoughts on the matter?
Thanks,
JR