in general I use whatever novak recommended at the time for gearing FDRs for motors as a starting point for my 1/10 scale stuff regardless of manufacturers and then go off of temp and performance. At times this also has topping out towards the end of the longest straight thrown in as well like I do with my 1/8 stuff.
http://teamnovak.com/tech_info/view_article/26
looks like FDR of 7 for 4wd buggy.
Any others using "torque" rotors in there vehicles? I am assuming that the classes are limit to "spec" torque rotors, no mod stuff in general that people are seeing or is more open by you?