SB Road Racing/Nascar/Sprint Car/Reving BUDGET BUILD

Say they make the exact same powerband/curve over 4000 rpm range 1st 2000-6000 rpm and 2nd 3000-7000 rpm then if geared right they should be fairly similar.

As for 318 vs 360, smaller engines then to make more usable power after peak hp cause is harder to under head them, which can come in useful at the end of a long straight or stay in a gear a little longer. Not saying that makes the 318 better choice.
so in the end the lower rpm and higher rpm power is really just because of the displacement and or class rules?