Re marathon vs 3P time - i ran 3:11 at London, which was a wee bit down on expectations due to a very hot last hour - most people I spoke to were 10 mins or so down on target. I think for a fresh 3P i'd hope to be an hour inside my mara time or maybe a bit more, but even without blisters my legs were suffering after half way. I've run quite fast 10ks and even half marathons 2 or 3 weeks after a marathon before, but I think a long fell race 13 days later was never going to be pretty.