In reply to adcat:
Eh up,
I'm a runner who took up climbing (specifically bouldering) to help me with my running and build up my core strength. I've never noticed it hindering my running but I have put more muscle on the top half, which isn't really needed on an ultra marathon.
As for giving up climbing to concentrate on the running, depends how much you enjoy each. I used to play football and rugby but gave up both to concentrate on my running because it meant more to me. It helps I was a fair bit better at the running, I mean who ever wants a 11 stone prop?