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

No the question is dollar for dollar, not 318 vs 340 in output, that's a given. Someone gives you a budget of 3000 and you need to build a max effort 318, same goes for a 340. Getting a 340 is gonna be 33-40% your budget. take what you end up with and run the formula. HP/$