I'm currently stuck with either 82.9 or 66.9 with the cog and rings I have on hand. I have parts in the mail hopefully arriving today or tomorrow that will let me run at about 74 or 75 depending on tire size.

(warning: shameless plug ahead)

check out the gearing calculator I'm putting together that is tailored specifically for SS/FG applications. It helps you find gear combinations in a bunch of different ways and also calculates how many skid patches each gear ratio has.

http://grit.homelinux.net/gi/

If you have ideas for improvements, leave a note in this thread:
http://www.bikeforums.net/showthread.php?t=175995