I've got an original Airhawk on my 06 GSA and it's brilliant. A mate of mine has the same fitted to his WC GS and it looks a little too big for the space. I hadn't heard of the R version until mentioned here but with the front cut out part it does look like it may fit better than the original Airhawk.
My advice to the OP would be to take a ride down to Bykebitz in Yateley. Offer both up to the bike and strike a deal with them
Some very helpful guys in there
http://www.bykebitz.co.uk/motorcycle-seating/airhawk-seating-system/airhawk-motorcycle-seats.html