I don't think you will even notice the slight drop in torque, if anything, you'll be gaining torque. Plus it'll sound much faster lol. That backpressure / loss of low end torque reasoning mostly applys to running open headers at the track. A good aftermarket exhaust will help everywhere, no matter where the tach needle is. Good luck on your shopping, and post back with your thoughts on it when it's done.
306 with all bolt ons, letter cam, ported E7's, T5 swap, full exhaust, 3:55's, 2" drop, and the worst paint you'll ever see or feel.
Dyno'd 300/316, 2745lbs-track scale
Best ET………12.4@108, 1.66 60ft on 8" ET Drags.