Well as for top speed, I haven't topped it out yet but I have a buddy w/ a Mach that claims he hit 150 w/ his 4:10's so top speed is surley not sacrificed. And at about 70 I'm turning like 2,600-2,750 RPM's, IDK an exact # because I'm not behind the wheel right now but on the freeway they're totally tolerable. Anything steeper than a 4:10 would be pushing it on the freeway. Good luck w/ the gears and let me know how they are when your done! I know you'll love them...