It's pretty well documented both here and elsewhere that R888s aren't the ultimate track tyre for the M3 or CSL.
Michelin PSC are the most expensive but they are supposed to be the best and i go with majority opinion when it comes to choices like that for track days - i have certainly had good experience with PSC and justify the extra £££ over lesser tyres whether 19" or otherwise imho
I also use Michelin PS2 as my road tyres for similar justification as they can also cope with some track abuse and are a safe bet when the track day is a wet one.
Tyres are one area that i want the best for my CSL...