I'm a big fan of deep dish wheels although I know alot of people are not keen. Ben has got CADES on his car which look good.
I would be a little concerned about going to 20 inch wheels however due to the tyre profile having to be so low you may find the ride would be a little harsh.
At the end of the day it's your car so go with what you like
I have some Vertini Monaco`s on order, should have them some time in november. Will get some Michelin pilot super sports fitted. I`ll keep the 326`s for winter. With suitable winter tyres, good riddance to the rft`s.
There's two ways you could go, deep dish or concave. Both with give you an aggressive 'fatter' look to the E89. Here's a few which I think hit the spot.