about 3000 at 65 IMO i think too many people worry about "high" rpms on highway, if its built right you will be fine. just like Rob referred to Mr Manner's comments
The best compromise I see is to use a 3.73 gear and 26" tires. * Starting gear ratio is 8.21 (not real good, but drivable) * 3000 RPM at 62 MPH * 5500 RPM at 109 MPH The result is that you will have to burn some clutch to get going while the Mustang launches hard with a 10-12 to 1 starting ratio.... and when you reach 5500 RPM at 109 MPH the race is over anyway. A 28" tire will get you 3000 at 67 and 5500 at 117 but then you will have an even tougher time launching from a dead stop. Get some granny gears that interchange inside your gearbox or swap for the M22 with the LOWEST gearset available. (Aftermarket tranny is easiest) With the LOWEST gear available and a 3.42 rear you will have tons of fun.