I built 3 S3 frames when I was consulting for another company, and I wouldn't touch the stuff - Especially not for a track frame or anything that was going to be ridden in an urban environment, or have the rear wheel skidded etc. If you were a lightweight climber on the road or a triathlete I'd consider it IF a customer really wanted it, but otherwise, the extra 100g Foco or 853 or similar provides makes a huge difference to the stiffness and longevity of your investment.

As I said, for the same price you can get a titanium track frame, which in my opinion is a smarter way to go.