Neither - wait for the CSLs!
Take it from me - I ended up getting some butt-ugly third-party wheels (not that the turbines are butt ugly!) for my winter tyres. It was a last-minute decision, I had planned to park the car in a garage during winter. That plan worked for two weeks - on a sunny December day I couldn't resist myself and took the car to a wheel shop and got the only pair of wheels they had left that fitted the Z4. They do the job, but the car doesn't look nearly as good as it should. On the positive side, winter tyres are rubbish and I don't drive much these days so it's no big loss. Fingers crossed snow will be gone in March though!
BTW I don't see what's so special about the 108s - they seem to be much more popular in the US and UK than on the continent?