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smaller will get you better MPG and will be easier to control smoke and EGT when towing. The difference in cost is mostly the supporting modifications.
I belong to the school of do it once. I would go with th ebiggest you can afford (whitin reason) and then just turn down your pump to be were you need/want to be. You can get 435's to make the same power at the same temps as 370's bur 370's wont ever make the power 435's can.
435's turned back to the same power as 370's wont hurt it. Hell it will probably do better because the pump wont be trying to push the fuel through a smaller hole.