Guys, he has a Venom, so he is using a BMW diff. I suspect that is where a 2.15 rear comes from.
JP,
I'm not familiar with what rear end gears BMW has available, but there are many gearing calculators out there that will allow you to play with the calculations. Here is a decent one:
Gearing Calculator.
I would look at how I drive and where are good places to require and shift play with to calculator to see what gear gets you close to what you want.