If you don't want a race but do want the miles, you could try the LDWA's Sussex Stride (late Sept); 50 miles circular over the South Downs, starts in Rottingdean and finishes with a full english fry up.
I'll be plodding round in my Milton Keynes AC top (black and orange); it'll almost certainly be the only one on display. So if you see a six foot tall 50 year old in an MK vest say hello; I might even have enough puff to reply.
My first 100 and the first half up to Washington was not good (mentally I was all over the place); after that (and with some wise words from one of my pacers) it got a lot better and I finally shuffled home in 23.30 or there abouts. many thanks to all those involved in putting this on; it's a hell of task and was really well done.
Cheers - Raymond
p.s. I'm very glad that being local to the east end of the course I didn't have any of the navigational challenges faced by some; that woulodn't have been any fun.