Just carried out the RS4 rear Anti Roll Bar conversion on the Avant, I must say how worthwhile it was!
VAGParts supplied all the necessary bits and bobs for £68.00 including vat and carriage.
All in all, the car feels better and imo how it should handle. Body roll in bends is reduced, the car feels more taught now and understeer/oversteer seems much more improved.
Very easy to do, all you need is a couple of jacks and axle stands (as you have to crawl under the car if you dont have a pit or ramps) some spanners and about 1.5 hours of your time!
I'd recommend doing it :beerchug: