All of the spread bore intakes are pretty close for performance potential, even EGR versions. If your little SBC is under about 500hp they will run right with any of the aftermarket dual plane intakes even the taller air gap Edelbrock RPM. You might see a little less top end power but they will make up for it in average and mid-range power.
Many years ago when I was drag racing my 1965 Nova SS I played around with intakes and found that on the "little" 283 a "modified" 1970 cast iron intake opened up under the carb to the apprx size/shape of an Edelbrock Performer or RPM was the overall winner for ET at the track.
Even with that said all the intakes I tested were very close, most being within .02-.03 seconds of each other and not much more than 1mph difference. The larger intakes shifted power to higher RPM's rather and gave up some short times to finish a little harder, so really not much difference or at least enough to worry about with that application.
The engine was bored .060" over, 12.5 to 1 pistons, 59cc combustion chamber heads, 260 @ .050" flat solid cam, TH350 with a 4400rpm stall converter and 4.11 gears out back. Shift points were 6500rpms and it went thru the lights just shy of 7000rpms running high 11's at 112-114mph.
I also owned and drove a 1979 K-5 Blazer for many years with a well prepared 406 SBC engine. I saw absolutely NOTHING playing around with intake manifolds and actually ended up staying with a 1978 truck intake that had the divorce choke set-up as I love the 1977-78 divorced choke Q-jets with the SMAB's. Since the vehicle was driven year round and used for hunting trips, pulling trailers full of firewood in Winter months, etc it preferred the cast iron intake in colder weather as it held the heat better than any of the aluminum intakes I tried on it........
