im pretty sure you will be better with an R1 in almost every possible respect. though the prospec is a fantastic deal right now as you get absolutely everything a $500 serpent or xray offers and doubled jointed front shafts i believe. I am very tempted to move my serpent onto another owner to get the prospec, but then i might as well move my S1 as well and get TWO prospecs ha.
really depends on what type of surface your on an the class. we race 17.5 on a parking lot and the s1 did just fine. we spray the track with sugar water and i had no problems with traction. the rear end was a little bit lively but i didnt spend a lot of time with the setup as my nitro car was being such a dirty bantch.
I finished second overall on the first day out with the S1 with nothing but a few changes to downstop and camber. of course, i set it up as i had my serpent, not the manual settings. so it might have been better if i had just surrendered to the instructions ha.