If you are comfortable with longer OCIs I'd recommend 7500. In my Taurus 3.0 I go 6 months independent of the mileage and in my Audi 2.7 Twin Turbo I limit OCIs to around 5K (which I would recommend for your high-revving S2K, unless as I said above, you are comfortable with longer OCIs). I think we have had people go successfully to 10K with GC (not in an S2K that I know of) but I just don't go that long.