You'll have to forgive me, your post seemed to emphasize first that you hate paying for gas because you drive 250+ miles weekly. I get that you want more performance for your economy, but more power will tempt you to open it up more often.
Regardless I support any decision most of those cars are awesome (Including the M
)
Using myself as an example.
My stock Spec V was fun to drive and I could see upwards of 37 mpg on the highway and around 25 city; thus averaging about 28-29.
My Spec V @ 300whp saw about 31 mpg highway and about 22 city; thus averaging high 20's.
Stock running around WOT all the time and running to redline. I was seeing close to 20-22mpg average.
Boosted running around WOT is like 15mpg. See how much this affects by increasing the power? More power = more fun = more fuel usage.
Keep that in mind when you make your decision.