What are the formulas to use when determing a brushless setup?

[lincpimp]

Unfortunately numbers are not the strong suit of this hobby. The mfg ratings are all over the place, and cannot be directly compared. So experience is the best bet. I know that a 10-12lb MT running 4s lipo geared for 40mph needs 150amps cont capable lipo. Go up to 6s and you can get away with 120amps cont. As Brian says there are just too many variables, so no set formulas...