Fox, I got greenstuff's fitted to my car about 2 months ago, they are definitely good pads performance-wise but I don't think any better than the standard BMW ones that were on before. They are a bit noisier but only when pushed hard - it's more of a hum or a groan and actually sounds quite nice, it's definitely not a squeal

*edit - they're only audible after 2-3 seconds of braking, and when braking reasonably hard at that.
There is definitely less brake dust, and it doesn't completely plaster over the whole wheel like the old pads (i.e. doesn't really cover my spokes, only gathers noticeably on the outer rim), but it's still very much there and it's not the massive difference that some people had convinced me of.
I think the yellow pads are the next step up? I've read in a few places that they should be considered in the large car/200bhp+ car segment. Which our cars just about enter into