Drew:
Here is a website where you can plug in the numbers for rear end, tire size and transmission ratios and you'll get the theoretical speeds.
http://www.368s.com/tools_rpm.phtm
The consensus seems to be to go with the .82 fifth because the .68 drops you too low for highway cruise viability.
0-60 without shifting is a little high. You would have to drop your rear end down to about a 2.88 which would be pretty tall.
I'm sure a lot of others will chime in with their ipinions on what you need so just hang on.
DonC