Depends on soooo many factors, surface type (drag races generally on flat tarmac sure but is it dusty, wet, dry, cracked etc?) Would 10th offroad be running control tyres or open choice? i.e spikes or 'slicks', how long is the course, which way is the wind blowing?
Also can't 10th off road run touring/rally body shells? I can't remember for sure but I think I read something about that in the rule book, don't think I have mine to hand. That would help even the aero side of things out.
But one thing is for sure, I think 10th off road is the only class where we can actually go overboard on the power, for everything else it's as much as possible really. I also seem to recall 2 speed gearboxes being allowed in a couple of classes, about 95% sure it's allowed in nitro on road classes, I *think* 8th off road can use them but not 100% on that... more than one speed transmission would be a major advantage.