The fan won't do anything for the power output. You're within healthy temp on the motor. With a 1700kv, there is not much a nitro buggy can do that you can't except for re-fuel and flame out. You should have more power, everywhere on the track except for maybe a long straight.

You might go through and do a factory reset (defaults) and start over on your speed control. Check your current limiter setting (I start @ 80%), throttle profile (TP1 or 2, but no higher). I know the RC8 has truggy-like gearing so it sounds like you're in the ballpark but could stand to go up another tooth or two.