RE: brushless without using lipo
over 4000kv is meant for on-road only use
4000 and lower is for offroad
Problem with NiMh in brushless RC's is the brushless RC's pull more power then the battery can supply leading to the battery over heating, and its lifespan being cut down drastically. Some people have even had their NiMh batteries get so hot the solder melted off that held them together.
You would need the top end NiMh packs, and then they might only last 20-30 runs before being destroyed, and their cost is pretty high as you could get 2 2s 5000mah lipos for the cost of one higher end 5000mah NiMh, but the lipo will last 200 runs vs the NiMh 20ish.
Also you will need to upgrade your rustlers transmission to the modern metal gears as the plastic would melt
As for traxxas's speed claims that is gear EXTREMELY high, running on a well groomed surface, and probably with the wind blowing in the direction its traveling. By geared high I mean you get 1-2 passes and have to let the thing cool down.
Outside that can't help with the gearing as I don't own a rustler