I saw a V8 convertible next to the new FRS at Ford in Harlow yesterday. As much as it pains me to say this, I think the RS was the more alluring of the two.
Both interiors are rubbish, no getting away from that: What the Mustang gains in the cool lever switches it loses to the Recaros in the RS. Ford could really do with hiring an interior design guy from Audi... The panel fit on the Stang was awful, some nasty sharp edges protruding into the front wheel arch on both sides where bumper meets wing, although the boot was an impressive size and the rear seats much more comfortable than you'd expect.
The RS has the lovely blue calipers, and some aggressive but delicate touches on the rear bumper/diffuser. It was the driving position that impressed me the most though. In the RS you sit cocooned, with the gear lever perfectly positioned and the viewing angles were excellent. The Mustang had the awful clicky buttons for paddles, slouched seats (even when adjusted) and worst of all the bonnet is so humped (why does the engine sit so high in the bay?!) that it's guesswork as to where the nose is.
Of course, it's impossible to take an overall view of the car from sitting in a showroom, but given that they're the same price I know which would've got my money yesterday. And that comes from a lover of RWD and a hater of the mk3 Focus.