What Andy says about being able to port the RPM heads later is true. A well ported RPM with larger valves will lack very little when compared to the 240 Trick Flow gains quoted above.
Lift..............Ported RPM cfm gain vs OOTB RPM
.100..........-7
.200..........+0
.300..........+9
.400..........+34
.500..........+41
.600..........+65
.700..........+60
