BULLSEYE, you're right about everything except "stock" handling, according to Road & Tracks Road Test Summary. The STi pulls an .88g on the skid pad,runs 68.4 mph thru the slalom vs the XF Limited that comes in with a .89g and a 69.6 mph slalom.
I know I'm "splitting hairs" here, but hey...we're bench racing, right?
Actually the whole thing is a moot point once you start modifying things anyway. Then it turns into "who can spend the most money, WINS!" I won't even go there, too many variables. Good Luck with what ever you do, I'm sure you'll have a blast with it.