Tried the Hardmoors 110 last year and got hopelessly lost - DO NOT LET THE COURSE NOTES BLOW AWAY! - leading to being timed out. Had a great time helping out with the marshalling instead. Terrific event and definitely stay for the breakfast on Sunday! Glad I'm on the flat this year though.
The majority of the course is packed earth and short grass. Some tarmac at the start and finish and around Milton Keynes. Worst area for water logging when I've done it was just before the tunnel at 20 miles. There's an interesting bit a few miles before CP4 where grip could be important (or you can just hang onto the trees). It gets a bit hazy but I also recall flint pebbles being particulraly irritating somewhere after CP7, but then lots of things were getting irritating by then!