Interesting stat brought up by the OP, never realised the H2H between these two was so lopsided at 13-4, always thought it was a bit closer than that...
Yes, that was my thinking as well. Very surprising how one-sided it is, and Nadal certainly has even more of a mental edge having won their last 5 meetings. That being said, Murray was faced by unfavourable conditions in each of those matches - two on clay, one on Wimbledon grass, and two on ridiculously slow indoor and outdoor hard courts (London WTF and US Open).
As guga says, this venue offers Murray better conditions (but not 'perfect) to play Rafa, and certainly you can guarantee that he will fight from start to finish to try to beat him.
My gut says Murray, so this will be interesting.