Z3M - S50 or S54?

[eng622]

Read the earlier post and noted pointers so is it worth paying extra (partly as car is newer) for an S54. Why does the S54 only have 325 bhp and not 343 as in the M3. Two cars with 19 inch wheels on PH, S50 (£12.5K) and S54 (£16K) and a further S50(£12K) on AT. Anyone viewed or know anything about these, first one says it has just had a new VANOS fitted.Does a car fitted with 19's give a much harder ride.

[eng622]

2001 X reg in blue at Wigan, so assumed it's an S54 (325 BHP quoted)