Ok, I get that.
Is there a reason, for not swapping rears instead?
-I took the liberty of doing some math, and found that 3.55s gets you about 48mph at 6500rpm.The overall starter ratio of 3.09X3.55 =10.97. If you were to use the 2.66 ratio, then 10.97/2.66=4.12s
The difference in the lows is about 16%. This equates to a change from 3.55s to 4.12 which rounds to 4.10s. Of course a substitution to 3.91s. would knock off about 300rpm or give you a few more mph.I would hazzard a guess that you have already done all this math, so Im thinking theres more to the story than just the low gear thing?
A simple change from 3.55s to 3.23s, would get you 48 mph at about 6000rpm, with the 3.09 low.