I was having a similar conversation the other day, and someone expressed the opinion that a 2.92 ratio (at least with a manual EA) might give best performance down the quarter mile. Most people think that 3.45 is best because the XR6s use them, but the XR6 was a complete package including engine and exhaust work.
The computer will not need changing, but you will need to replace a part (speedo sender?) in order to get an accurate reading.
Jack Travis, E-Series Acting President
1989 Ford Fairmont Ghia turbo/GL replica (underway)
1994 Eunos 800M
1990 Ford Laser S