I tried something similair to this in last years tamiya series.
With 4500mah packs my car weight aprox 1560g. With 2400 nicads I had to add about 80g of lead to just over 1500g.
The car handled a little better but accelleration was noticably less. Speed difference was most at th start of the runa nd towards the end I started catching people up again but it wasnot enough to be an advantage.
If I had not had to put the weight on it might have been an advantage but I think probably not because you would still have to overtake people later int he race.
MRT, Novak, Spektrum, Sanwa, Tamiya, Alleven RC, Maxamps, CheapBatteryPacks, Duratrax Ice, Pro Peak PSU, Nuova Faor, McLarney Racing, Futaba, KO Propo, Team Associated, Enerland.