How are you getting 75mph at 2600 RPM?I guess, choice of differential ratio is personal preference and how you use your car. Also, larger displacement engine (I run 2.5) provides plenty of power and torque for brisk acceleration even with standard differential. I mostly drive long road trips, so when I added Quaife LSD, I made special effort to keep standard 3.44 diff ratio. Two days ago I drove my GT eleven hours from Pennsylvania. I certainly enjoyed keeping 75 mph at some 2600 rpm. But for smaller engine short ratio could certainly be fun when jumping from traffic light to traffic light or for the track event.