Just a quick note on the excellent service, quality and value that I got from these guys today. I traded in a set against a set of brand new CS Performace alloys. Very happy with the wheels also - had a close look at them out of the box before they went on the car. Looked to be very high quality engineered and finished rims.
I went from 19" AC Schintzer Type 4 (same size all round) fitted with non-runflat 235/35/19 Hankooks packed out with spacers (came fitted to car when I bought it). I didn't like the look of the ACs particularly - although great wheels, on the car I didn't like being able to see the rusty hubs and from the rear the 235s looks skinny - accentuated by the wide spacing of the wheels.
I went to the BMW standard 18" spec of 225/40/18 front, and 255/35/18 rear. Went for Avons, again non-run flat. Compared to the 19", as you probably imagine, ride is noticeably improved as is road noise. Steering feels more positive. Grip (once tyres scrubbed-in) feels more progressive / better feel. I feel just as confident, if not more, at the limit of grip, taking favourite bends at same speed. The 19" tyres were quite new with at least 4mm of tread and correctly inflated. 18" works better for my driving style and roads and I don't think the car looks much different - 18" looks equally at home, nice and snug in the arches. Having them on the car, different styles aside, I'd even argue that 18" looks better.
Pics of the CS Performance 18" alloys-