Don't know about Stone, but I use GT3 type arms with shims for camber adjustment like these:
RSS Tarmac Series Lower Control Arms - RSS
Other advantages over camber plates are increased front track width as you add shims, and caster adjustment if you buy them with the bushing centers that rotate.
These arms are mostly for the front on our cars but are also a fairly cost effective way of eliminating all the rubber bushings in the rear when you add up all the parts and hassel of changing out the rubber bushings in OEM control arms. But, you really don't need them in the rear for camber.
If you are hooked on camber plates, I beleieve there are some tricks to get more than -2 degrees of negaitve camber out of them. These tricks seem to involve either drilling a larger center hole at the strut tower, or putting shims between the camber plate and the strut tower so that the strut center bolt has more room to move without hitting the body. If you look around on planet-9.com under the 987 competition driving section, you can find more info on how to do this. (FYI, in general there are a lot more Caymans that are tracked seriously than there are Boxsters, so you can find a lot more track info there. The 986 and 987 suspension designs are identical from what I can tell)
To use your existing wheel sizes, I would put the 8's on the front and 10's on the rear. You can forget trying to fit 11's unless you want to hack up your body work. I normally use 8.5" or 9" at front, and 10" at rear with appropriate size tires.
Good luck.