What's the chainstay length on your bike? I would suggest you look for panniers that have adjustable mounting clips and definantly bring in the bike for a test fit.

FWIW, the chainstays on my mountain bike are 42cm and I have no heel strike issues (I also wear a 9.5 shoe and the bike has 175mm cranks) with Novara Transfer panniers. They have adjustable mounting clips and are longer than they are wider (I had heel strike issues with all of the wider panniers I tried).