Here's another site for figuring rear end and transmission ratios. It talks about the split between gears and what to shoot for and what to avoid. The 600TKO with the .82 5th gear seems to be the one to go with. There was a previous thread about the TKO with the .64 and those with it were complaining that it was too high and bogged the motor under 70-80 mph. Some have changed from that one to the .82 and were very happy with the results.
www.secondstrike.com/Technical/GearCalc.asp