SX3 Pro vs. SX3 S1
 

So is the only difference the carbon fibre parts? The S1 should go just as well on the track?

http://www.racing-cars.com/pp/Car_Showroom/CAT_SX3.html
according to web site just cf parts that are different
CAT SX3 S1 version includes;

• S1 Composite Material replaces all Carbon Fibre components.
• All further spec's the same as Pro C/F Version.

Yup, so apart from the bling factor and a slight loss in strength, the S1 should be just as good on the track I guess.

If not better on low grip/bumpy tracks.