which gear would be best?

[doitbby]

I am ordering a keisler tremec tko 600 and was wondering which rear end gear would be the best. I was thinking 3.73 or 3.91. any suggestions?

[Aussie Challenger]

  We will need to know what motor is up front and what modifications have been done and what you will be using it for, rear tyre size would also help.   
  Welcome to the site   

[doitbby]

the car has a 440 6pak,.60 over, mild cam,msd ignition, headers, magnumforce front end, wilwood master,6piston front, 4 piston rears. the tires are 28.1 " tall. I have 20x10 rrims in the back and 19x8's in the front. thanks for your help

[Bullitt-]

Here is a link to a 6-speed calculator on Excel.  You can open & enter your values, if your tranny has different ratios "unprotect" the file & save to your computer. Change the ratios to match your tranny & you can see speed & RPM's for whatever rear end you care to enter. 
  I notice the RPM's stop at 3300..You can insert extra rows, Hold &  drag the last row down & it will copy to go as high as you like.

http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls