I went with the Flowmaster Force II on my Expy. You'd never know it was there between 65-80 mph, but if you really get on it, you will turn heads. Otherwise, it just sounds nice in normal operation.

 

Bought my truck used w/ 24k on it. Previous owner put a catback Borla on it. Love the look and sound. Problem is the pipe going into the muffler recently broke off flush at the muffler. Supposedly a lifetime warranty from Borla but I have no receipts. So if it can't be welded, I may go with the 50 series flowmaster and keep the Borla tips if I can. The guy at the custom exhaust shop I spoke to won't even sell Borla due to cost. Said the Flowmaster gives the same performance for much less.