Well as Stevo Knows i own one and it has the Wing backs and i don't have any problem with them and I'm by far from a small person at 6 foot 3 inches and carry a lot more weight at the moment than i normally would.
Ioksotot engine wise i guess you mean 4.2 not 4.7
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As for discs you don't have to buy Audi ones Theres loads of other companies out there which sell different styles because the later B8 discs and the R8 models use the same discs Just the wavy design instead.
Brake pads are not cheap but no more expensive to be honest that a set of race pads for the coupe. I paid £200 for my last set and its done 10K miles last year and they don't look to have worn at all even with some very spirited driving.
Cost of up keep is no different to any other car just get service yearly and get stuff replaced when needed don't hold out or it will mount up just like any other cars
Ref the B8 shape S4 i wouldn't touch it because of the body styling just isn't the RS model with the wider body plus its a V6 so you don't get that screaming 8400Rpm to play with.
Stevo The Red is a very nice colour and came as an optional extra if i remember rightly
In all the B7 RS 4 will hold its money more than the B8's because its the last manual Audi RS they are bring out and the true RS fans are still buying the B&'s over the newer models.