Performance wise you should see a small gain. I noticed a little more oomph up top. I think it still sounds good with the stock GT mufflers. Much better than the stock v6 exhaust.
Backpressure problems are no issue. Also, there is no loss of torque, rather peak torque merely moves up a little in the rpm band. So it "feels" like you've lost a little torque down low, but not much. Well worth it overall IMO
2002 Mineral grey GT 5 speed. Flowmaster 40's catback, Mach 1 grille delete, timing advance, push button starter, Bullitt pedals, FR500 steering wheel, K&N FIPK, Self ported upper intake w/ spacer, Pioneer Avic D3, MGW shifter, MM FL subframe connectors, Mach 1 springs, Bilstein HD struts/springs