RT660 is probably the best choice for AX only on a Boxster right now. They're like the re71 but a little more forgiving at the limit. Horrible in the wet though.
The A052 is a little faster on cars with decent camber but likely not worth trying on a stock Boxster. Fast fast wear.
RS4 is slower than those two but still a good AX tire, great HPDE tire, and better wear then with of the two above.
New Bridgestone RE71RS just came out, nobody has run them yet
afaik. Supposedly more track focused than AX.