In reply to Tony the Blade:
this is a bit like the rock shoe conundrem (um spulling!!) try on and find what you like
done a few mountain marathons (about 10) and alot of fell races and my choice is inov-8 mudclaw 270 (not the newer 330 that are heavier, i really swaer by them, aggresive, and shed water very well.
I used to use walsh pb but they crucified my feet, however alot of people say that the inov don't fit that well around the heal and aren't as durable as walshes. so horses for courses
makes i would recommend to look out for are walsh, mountain bear and inov-8 (though not all their shoes are fell shoes check their suitability sheet on website), or new balance rx, i would suggest wearing something with a really aggressive outsole like the pb or mudclaw, it will really give you confidence on decent, and stick like sh1t to a blanket on the up hils, and specialist feelshoes like these seem to shed water better, and they are usually designed for british conditions rather than french, austrian, swiss or us, that are very different, like salomon, north face, timberland.
size wise, i personally go for a half size bigger than normal, though this will be explained by the shop you try them on at, with at least a thumb width extra length as your feet will swell up alarmingly over the weekend and it should hopefully then prevent painful rubs
and lastly don't bother with a gore-tex lining, your feet will get wet about 7 o'clock saturday morning and eventually dryout somewhere south of scoth corner on the drive home on sunday, and gore-tex won't won't make it any better!!!!!
apart from that, you have a cracking time and i hope you love it
other views are available on the fra (fell running association) website on their forum!