Which Carb Gives a Balance of Power & MPG?

well i picked up a performer rpm since i couldnt find a performer for what i wanted to pay. i guess im going to weld it up, offset the bolt pattern to center it over the square bore opening and hog it out to fit. the secondaries hang over the flange about 1/4" on each side. ill probably weld up a choke pocket over the heat crossover too. well see.