Bugger. My preparation for this got off today with a 70 miler around a similar area, south Birmingham to Worcester and back, with disappointing results.
The distance was hard but I have no doubt that I can do a 100 without too much stress, but what has killed me was the speed. I normally manage close to 16 mph on shorter 15-25 mile runs, but this was barely 13 mph by the end. Was the hills that killed me plus the wind didn't help, I'm not used to anything like what I saw today.
Since the bronze completion time here is about 15 mph, at my speed it looks like everyone will have packed up and gone home by the time I finish. Like I said, bugger.