Hi
Up to you really, the Pro S 5w-40 is better suited to track use than the X-Cess, but it does cost more. Gulf Competition is very similar to the PRO S, but costs about the same as teh X-Cess, so that's a good option.
http://www.opieoils.co.uk/c-656-5w-40-engine-oil.aspx
Cheers
Tim