I have 3:55's on my GTX, stock converter and 295 50 15's. Im on the highway a fair bit and its fine to me. im considering going to 3:73's. Any higher with my size tire would suck on the highway. 3:55's are about as high as you'd wanna go imo. My Challenger had 4:10's and that was horrible. People passing you looking at you funny because you are struggling at 50ish. No thanks.