ESP w/ what you describe
things that knock you out of STX are the intercooler hose, ecu tune (in STX you can tune the ecu but only for timing and A/F- can't touch any of the boost paramters
the other "sticky" thing is there are new rules (actually a "clarification") concerning emissions- the old rule said you had to have one cat in place (didn't matter which one) and could be no further downstream than 6" of the furthest oe one. Now you can't run any cel defeaters- either mechanical or ecu- which people are finding out generally means running two cats (w/ the O2 sensor behind the last cat), in addition the have deemed the egt probe in the uppipe as emission equipment needed- so that means a gutted stocker or an uppipe w/ a provision for the egt probe.
the clarification basically sucks and has a lot of WRX folks migrating out of STX- which was probably part of the plan of the "clarification"
ESP has traditionally been the pony car class- camaros/mustangs- when fully prepped they are very formidable. ESP has no limit on wheel or tire width and R compounds are allowed.
What I like about ESP is that it matches up nicely for a car that is going to be used at the track- allows uprated radiators, uprated intercolers and you can fully tune the ecu including boost parameters.
