Stock 340 intakes

I noticethe comment concerning a 340 stock cast iron intake as being limited by RPM and flow!! in the world of stock eliminator, the cast iron intake will and does make power. most 340 stockers are pulling 7000 +RPM in the traps.
the motors doen't seem to be laying over either. so if it's that bad, then 5500 RPM would be the limit. granted ,after market aluminum should work better?