I have an old Savage and do not have a problem with the drive train. Most of it is still what it came with over 8 gallons ago. I did set it up and make changes for racing but the drive train is pretty much stock! Yes the Fire Storm will be faster then the MT do to weight and being 4-wheel drive but the MT will out handle it do to being 4 wheel drive. I all so do not recommend the RTR as it has very weak differentials and the SS kit is MUCH better with many up grades the RTR does not have but should!!!!!!!!!
Did you look on HPI web site to see what the difference between the two engines is?