I did it earlier this year on a road bike. Most of the off-road bits are well surfaced and no problem at all for road wheels. I did make a couple of diversions from my intended route when it all got a bit too agricultural, but that was a result of shoddy planning on my part. When I did detour, it was easy enough to get back on track, as the signposting was very good indeed.
Had a cracking time... I'd certainly do it again.
