9 time out of 10, the S300 delivers a better result. (Better cold start, idle, sharper, crisper & 2~3 hp more everywhere)
Though on one occasion I had an FC outpower an S200 on a DC2R
(But I suspect there was an issue with that ECU)
S300 has quite a few extra features not present in the Apexi. (So for track use is way better)
That said, the Apexi is still a good thing & well worth it for a roadie, particularly when purchase 2nd hand.
But must be tuned via laptop for better than 1/2 decent results