Just to close out this thread, at least for me, I ended up picking the AA8 piggy-back tune. The guys at GSR were very helpful, but I just couldn't get my head around a mod that couldn't be COMPLETELY undone if required, since the car is very new, and I don't yet know how mod-tolerant my dealer is.
I wrote up the install here...
http://www.2addicts.com/forums/showthread.php?t=1233814
It's only been a few days, and the car is still adapting to the tune, but so far I'm very happy.