If you post your rear end ratio, tire size, and tell me if you C4 gearing is standard ratios I'll print you a nifty chart you can use to compare. If you are considering different rear end ratios let me know which ones and I'll print you up a chart lke this
http://www.2mfffabshop.com/gr/r62_350_2754017.htm
http://www.2mfffabshop.com/gr/r62_350_2754017.htm
Here is a chart that allows you to plug in a number of combos and compare:
http://www.drivetrainsuperstores.com/calculate.asp
http://www.drivetrainsuperstores.com/calculate.asp