It's funny that I kind-of stumbled upon this thread because I was running my XXX-T MF2 today with a "frankenstein" battery I made out of 5 new cells and 2 old cells(7 cell Ni-Cd 2400). I guess the 2 old cells were bad because I got 1 or both of the old cells to vent. I wasn't even running it hard. I checked the temp on one of the old cells and it was 300+ F.
the new cells were only like 130F.
Anyway...yeah I think you either need to lower you gear ratio or get a battery with a higher discharge rate. If you want to stay with Ni-Mh you should probably get the biggest capacity pack you can find. If you want to go with li-pos you'll be impressed with the difference in power throughout the charge. The voltage of Ni-Mh packs tend to sag alot more under load than li-pos.