If you're going with Kumho's, I'd say go for V710's first, then V700 VictoRacers (not Ecsta V700's ... I've heard they're not quite as good as the VictoRacers).
Initially, Toyo R888's weren't made in a 315, only a 275, but they recently added 315's to their list (
http://marktg.toyotires.com/file/30029.pdf). Some people have been complaining they're not getting the same performance from their R888's as the old RA1's, but apparently R888's need to be run at lower pressures than RA1's used to be.
The better/best options, IMO, are Hoosier R6's (or A6's, if you're doing Auto-X only).
Also, BF Goodrich makes the R1. They're supposed to be pretty good for a track tire as well, probably comparable to the R6's.
You will find that on the track, 275's in the front and 315's in the back isn't ideal. I know because that's what I ran this year (Hoosier R6's). The car pushes BAD into the corners, especially tight corners. I can only imagine for Auto-X that it would be even worse!
I also have a set of RA1's, all 275's, and they're much more "balanced" in terms of good turn-in, and allowing good rotation of the rear end. But they're nowhere near as sticky as the Hoosiers.
__________________
2002 Z28: A4 --> M6, 3.73's, headers, Strano suspension (HP3).
Best E/T: 12.878 @
110.15,
1.940 60' (w/M6, 3.90's, LT's).
Stock E/T: 13.434 @
105.80,
2.152 60' (w/A4 & 2.73's).
1973 Camaro:
(Dad's) - 355, TH350, 4.10's. Best E/T: 12.795 @ 109.72, 2.159 60' (M4 & 3.42's). 1981 Z28: 383 c.i., TH350, 3.42's - sold
August, 2000.
Tire shoice? 
