Today, dollar for dollar, is the 318 faster than the 340 ???

If we all had unlimited funds we would usually just go out and buy exactly what we wish for first choice. So there then comes the hot rod mentality, and that is what makes life fun and challenging. Build as good an engine as you can for what you can afford and what is available.
I understand up North old cars rust out and not so much wear out mechanically. Down South , they can do both but not like in the salt belt. Back in my home state of Mo. 340s have been scarce and expensive for the last 15 years. And to find one not bored out to an inch of its life..well.