It is the big track - scary, scary, scary! I'd probably take the ST2 since I could hide behind the windshield at those kinds of speeds (I used to hit 125 in my Boxster at the apex of Turn 8, then drift out to the edge before braking for 9 - it is truly frightening to me). However, doing the slow group and just taking it at your own pace would be nice - no speed limits, no cars, plenty of runoff IF something happens.
Mark