I got a rear axle from a Mach 1 for my wife's 02 V6. 3.55 gears, limited slip, vented brakes, quad shocks. It's about a 8.5% increase in torque at the wheels in any given gear. I used a Diablo programmer to correct the speedometer/odometer.
Since split port 3.8's have decently flat (enough) torque out to their redline I think 3.73 might be better at least on an automatic (14% deeper than 3.27) but the Mach 1 axle is such an easy afternoon bolt-in that bundles several improvements in one job that I think it's the way to go for upgrading a stock V6 with open diff 7.5" axle.