Leave the exhaust how it is - twin 2 1/4" is perfect for a V6, even when it's pushing decent numbers. I had tryed a few exhaust combos on my old VS which was stroked and supercharged and the twin 2 1/4 was the best all round, especially for midrange torque. If you want to pick up a kw or two up top and sacrifice a decent chunk of torque, then go bigger, but for a street driven car you want that torque.
Quagmire: My fellow Americans, I have not been entirely truthful with you. I did gagoogidy that girl. I gashmoygadied her gaflavity with my googus. And I am sorry.