lee,
from my limited experience, adding weight to a LiPo powered car (in a mini) will be a great disadvantage as you will be out of reach to chase the NiMh guys (especially on the straight)...all other things equal. But the downside is, as rightly pointed by many, the problem of traction roll..thats the challenging part...with a LiPo ur style of driving needs some fine adjustment...
never give up... keep on working finding the right setup for your car... i am still finding the sweet spot (tuning wise) for my car...with various selection of tires...
altho' with some frustrations along the way (coupled with my so so driving), m-chassis never seem to fade away and with my two other buddies (also running on LiPo) we had lots of fun bashing the car...
plus, on the maintenance side, LiPo is a no brainer thingy... we have had bad bad experiences with NiMh (even with proper maintenance etc)... but then again, its history...
*you might want to try foam tire upfront with a 40 shore rating... tire needs to be trimmed down a bit for that rollout...*
we'll see you in a months time for the Melaka race...