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

I guess it boils down to budget and availability. I can only speak for myself. If I had a free or low cost 5.2, then Oregon regrind. 218/224 .530 lift. Airgap clone. 650 Edelbrock avs or whatever could be had on the cheap. Summit 1 5/8 headers and go have fun.

Magnum heads outflow any stock LA head. Of course, porting changes everything. I don't need to compete with a "built" 340. 300-320 makes for satisfying performance with bolt on parts.
If I'm going to buy new pistons it will be a bigger motor. I rented a vehicle. 300hp v6 Challenger, and boy was it much fun.