I did it two years ago and in 3hrs 38mins. I had not cycled much at that point. The running was really hard, the second time round was a killer. Train your butt off, I think you need to do the 16miles of running quite regularly to give you a reasonable time. The brick sessions are also a good idea, maybe go for a run after the club ride, take in some hills and feel the pain, that is what you are going to be putting yourself through.
I don't think I will be doing it this year as the memories of the first time still have not gone away.
Cheers
Marek....