autox killer = http://www.redshiftmotorsports.com/SearchResults.asp?Cat=12
an EF in STS with the right setup has proven to be a winning car. Now, since you aren’t worried about winning, then I suggest an EF Si, Koni’s, and tires. You can stay in HS, and have a competitive car that’s fun to drive. It won’t be the fastest thing out there, but a slow car will really help you learn things like driving the right line, and speed maintenance. You can also take that EF, and do it up a little more and make it an STS, FSP, or SM car, and still have a ton of fun with it, while still being competitive.
Like Jeremy said, TIRES! They will make the biggest single difference for autox.