I went with dual 2.25, flowmaster 40s and an h pipe. Anything larger will lose more torque. It shouldnt cost more than 450-500 max for a shop.
-Mac CAI, 73mm Mass Air
-Dual Flowmaster 40s, H pipe, 2.25 in pipe
-42% Underdrive Pulleys
-4.10 Gears & Trac-lok