I think there are two expectations butting heads here a little bit: the desire for a 100mph+ speed demon, and the desire to keep things simple. On a good note, a 1/8 buggy is a pretty decent speed demon platform IMO, and a 1/8 on-road GT is only a few parts away. Plus, as people have mentioned others, including the RC mags, have got 1/8 buggies going pretty damn fast without too much work. However, if you look at the extreme speed vehicles, almost all of them are VERY heavily modded, with custom parts, sometimes barely resembling the "base" chassis at all. So it's up to you to decide where in that spectrum you want your vehicle to be.

I agree DrKnow, I don't think the Slipperential is really in the cards for a speed machine build, I was just posting the link since he asked about it. I could see it possibly being applied to drag racing for launch control (using a VERY tight slipper setting) but it could just as well just slow you down (more rotating mass than a regular center diff). I don't know much about drag racing, if you want the tires to break loose, or not? Most people do look at the Slipperential as a drivetrain protection item (which it is) but it's equally a traction control tuning aid.