I don't think the Senton is the best choice if he is trying to stick to SCT rules. Most tracks require 2s for racing... the Senton's 2050kv motor will be very slow on 2s. Also the 17mm wheel hexes are not allowed in most SCT racing. If the OPs tack has no electronic/wheel hex requirements then the Senton would be ok.
Out of the 3 the OP listed I would go with the Losi or SC10. No reason a good driver with the tenacity shouldn't keep up with most people on the track. Unless you race at a pro filled track. The 3800kv 550 motor packs a good punch. Just upgrade the servo and the turnbuckles.