Lesley, it's a hard race, especially if it's warm (as it was this year), but a great one! The best way to know if you can make that 3hrs 30mins cut off is to go on one of the many recce's that take place. I ran around it a couple of weeks ago and intend to go up again next month if you're interested?
Good point made by Stolly, it's alright getting to the cut off time of 3hrs 30mins, but it's still along way up and down Inglebugger!!!!