definitely the better and better looking brake calipers, I really notice this now I've changed the wheels.
I mean it costs about £1000 at least to get a brake upgrade.
But also the better Diff, the 7 speed DSG box, and people apparently the exhaust is different, sounds better

So just seems a lot of upgrade for £1000.
It's the only extra I would consider.
But saying that, I don't think you need that diff, not unless you drive like Jeremy Clarkson

, I find that it flys rounds corners as it is, and also it's something else that could go wrong in years to come.