trouble is that there are so many different types of race. Road, off road, track. 12 hour, 24 hour 48 hour. Different people seem to favour different types of race. For instance, I help a GB runner who is great on the road and track but is not so good off road mainly because he has developed and ultra shuffle that isnot suited to uneven ground.
For the UK the names Mark Hartell, Jez Bragg, Sharon Gaytor and Lizzie Hawker come to mind. i'm suer there are others that people can think of.