This the engine I got the 380hp 5.9l Magnum which dyno 409hp at peak and only varies 14hp from 5000-6000 rpm, but under this torque doesn't take over, when your under 5000 rpm torque is not now the power your using it's whatever hp @ rpm your at during your acceleration aka 230hp @ 3000 rpm, 333 hp @ 4000 rpm, 396 @ 5000 rpm, 409 @ 5400 rpm thats what moving your at those rpm's. If your engine is geared so you spend almost no time main powerband 4000-6000 rpm and spends more time in the 3000-4000 rpm range it's gonna act more like a 333 hp engine instead of a 409 hp one.
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What I get from what your saying, Is say a street car is idle-5000 rpm you want to peak in the 5000 rpm area. So since rpm is fixed There's only one main way to increase NA hp which is torque and Torque is mainly a product of displacement which is where the saying Torque is King, No replacement for displacement etc.. so yes a well put together 318 and 340 in these rpm ranges peaking at the same rpm the 340 will have a stronger hp and torque curve through the whole power band.
But still whatever part of the rpm range your talking about off idle low mid high well over peak power etc.. it's hp moving, accelerating towing crusin etc.. your vehicle which is the combed effort torque and rpm, torque is one powerstroke and hp is all of them added up per minute aka rpm.
But If were building to the same hp then the power "hp" curve could be the same but the rpm's will be different, cause everyone goes on about static displacement aka non running engine 318 340 etc.. but a running engine displacement is dynamic and we measure it in cfm's and a 318 needs more rpm to displace the same amount of air maybe 0-800 rpm more depending how well built and yes a 318 will need more gear and stall etc.. but doesn't automatically make it a race car now depending on what power level were talking about.