I just spent ~8 hours making custom spacers and fitting some ID CTX 6.5cs in my 2011 http://www.sonicelectronix.com/item_...CTX-6.5cs.html
TOTAL waste of time IMO.
Pros: They are a bit cleaner, not as harsh up top
Cons: Way less bass, quieter
Granted they're only being powered by a AVH-P4300DVD at this point. They'll sound better once I amp them. Only reason I did it is I had them from my '05 STi.
If I had to do it all over again this is all I'd do:
New HU, AMP the fronts and a 12 sub and call it a day.
Biggest bang for the buck so far has been matting the front doors and the HU.