Thanks Justin for the most correct answer to that question.
Cribbs: If you have an auto, go 4.10. If not, 3.73. RPM at 70 will be perfect either way. These are the gears Ford should have installed at the factory. Enjoy!
Well I won't express any opinion on which gear to get, because that is like pissing in the wind here lol. But my RPM's at 70mph on the highway in 5th with 3.55's is around 2100-2150rpm (with 18" wheels and a 35 series tire)
I love my 3.73's but anything is probably better than the 2.73 wagon wheel it replaced. either gear is gonna feel like a kick in the butt. my rpm in 5th really didnt change much, makes the most difference from 1st to 4th in my opinion.
I noticed a difference in RPM going from the 2.73 to 3.73 (prolly around 2400-2500 RPM at 70), but the difference leaving the stoplight was phenomenal. Just depends on whether you want a top-end car or a dart off the line, I guess. See guys, I am learning a little of this "gear-head" $#!^,
it depends on what you will do with the car... the allfordmustangs page that was posted above also has an optimal gear calculator for the 1/4 mi depending on your trap and unless you are trapping around 107+ it is pointless to have anything less that 4.10's (according to them) then u just have to decide whether the higher rpms are gonna bug you on the highway. and last but not least. the SOTP feel between the auto and stick is usually thought of as being one full step (i.e. 4.10 auto feels like 3.73 stick...) so a general rule of thumb is 4.10 auto, 3.73 stick, even though thats not optimal for the 1/4 mi. but maybe a streetcar...