RE: Want an Extremely Fast Car or Truck
Out of the three that you have listed above...the HPi, Associated, and Traxxas, I would go with either the Associated or HPi...they will handle much better than the 4-Tec...and there are parts available to install a "Big Block" in either of them.
I have a couple of NTC3's and an RS4/3 SS and they handle pretty good...so either one of those should be o.k. and if you put something like an .18TZ in it, you won't have to change the motor mounts and it won't throw the left to right balance off too much either...a "big inch small block" is the best over-all package IMO.
If you're not much interested in handling, then anything goes in the power dept. and you could theoretically put a full race "on-road" .21 or a high perf. "truggy" .28 or even a .30 or .32 in one...but be prepared to break stuff...(driveline components, etc. )