I would think that even though the 2.5RS is a great car for STS and has the advantage that the SVT cant overcome, the LSD. Otherwise I would say that a well preeped SVT would be the better car. As far as the WRX well the power advantage is lost.
I would say that I feel the best car for sts WOULD BE A 328 BMW well prepped, motorsports diff and full suspension. IMHO!
In the end I am always about 6 full tics off the first place scooby a few more scoobys ahead of me as well, then there are about six or seven behind me. Hey they win by sure number!