Right - quick update having put about 500 miles on each (!) car over the last few days
Looks are always subjective of course and the Audi is not in the best spec/colour - there are better that suit the car better.
Here are a couple of pics of the previous RS5s I have had
Personally I do not think the BMW looks any better than the audi (although I do love the BM's wheels). The first M5 I saw at a different dealer was the same colour as this one and I just walked passed it thinking it was just another 520d M Sport
The BM is clearly a formidable car........in the dry !!! In this recent weather it has barely any grip. combination of poor roads, Michelin Pilot Super Sport tyres and turbo engine power delivery.
It will easily wheelspin (or try to) up to the national speed limit (and a smidge beyond) and a couple of times even on part throttle overtaking maneovers the back would wiggle which all in all is a bit un-nerving.
The Audi, despite only having 450BHP, just does not break traction at all despite how cruel you are to it.
Economy probably about the same at c20/21 mpg (did get 25.5 out of the audi on a motorway run yesterday)
In the dry the BMW is agruably just too fast for these roads
So overall I am glad it is the Audi (RS4) that I have my money down for next year and there is no way I would consider the M5 in this country with our variable weather. If the rumoured 4 wheel drive car came out then that would be a much better prospect.