I like your thinking.. I am actually thinking of a set of 4.10's. Afterall 6th gear is great on the highway.. and 1st gear goes up to like 50mph if you go up to 6500.... which any drag racer will agree that if your 1st gear takes you to 50 , and you have 4 gears to go thru in the 1/4 (assuming that you are running 125mph or less), the 3.55 are hurting. I would guess that going from 3.55 to 4.10 would pick up 2 mph, and .1 or better...
I am not a bench racer, I have owned several 10 second mustangs. I have a set of 4.30's in the garage that I am going to sell (I had them for my last project) and prolly get a set of 4.10. I would like for someone to tell me what rpm they are at in 4th gear, with 4.10's at 50 mph.
Don
I think that 3.73 would be good for your car. It just depends where your power band is. On most mustangs the 3.27 they come with are the perefect combination of highway and performance. On a tbird a 3.55 ratio would be better because of the taller tires. It would be equivlent to 3.27 in a mustang.