Hey Rich! Rupp is running a Viper T56 (or was last I checked) that probably has a similar gear ratios w 3.89s. That car's a little zippy
I'm running the closer ratio (2.66 first/.62 sixth) and 3.70s on my LS7. Not on the road yet, but I think sixth will be mostly useless below 80 on 26" rear tires.
Edit: There's a number of calculators out there:
http://www.5speedtransmissions.com/gear_calculator.html