Just for reference, the link below is an sti with 18x9 +63. Which is 12mm further in than a 18x9.5 +45 or 9mm further in than a 18x9.5 +48. I don't know how much the strut clearance varies on the GR WRX vs GR Sti but with minimal negative camber I'd guess you'd be ok.
http://www.iwsti.com/forums/gr-tires...ring-rf-2.html