Not done the race, but I know the hill very well as this is where I train. It's not as long or as much ascent as the Wycombe half hill, but steeper for part, rougher underfoot and with even less warm up. That said, its toughness really depends on how much hill training you do! We did pretty much the same hill 3 (or was it 4?) times in the Bucks XC champs back in January!
My question about trail shoes was more aimed at the Bradenham end of the route which I don't know very well and the balance between overall off-road and road on the route , but personally I'd definteily want something a bit grippy for the grassy downhill at the end if its damp so if its raining or just rained I think I'll plump for trail shoes anyway.
See you there!