Mark - give it a go, particularly if you've kept up the running since the 10k in June. I did my first ten miler a couple of months after the first 10k, and although the last few miles were quite tough, I got through it fine. :o)
Going back to the earlier emails, it made me think back, and how I never believed I could run some of the distances I'd heard people speak of "in legend", but gradually I built up the distance I could do. After my first 10k I just didn't know how anyone could run 10 miles, but a few months later I'd done it, and then gradually built up to a full marathon. I think it's all relative - however far you've run, the next step up will seem long, but later on you'll think of it as a short run!
Congrats to all, whatever stage you're at - hope to see you guys at a race sometime :o)