I did the long route last year on a Planet X London Road with Schwalbe g-one 35mm, finished in the top 30, and I felt pretty beaten up at the end. If I was doing it again this year in similarly dry conditions I would probably use the same bike with 650 x 42 WTB Resolutes tubeless at 25/30 psi.
There were a few sections I had to walk mainly due to the rough terrain but also due to fatigue. You will walk less on a hardtail and fly down some sharp descents on a full suspension but overall I think you will be faster on the Pickenflick if it’s dry. If it’s wet and muddy I would probably ride a hardtail but maybe not a single speed. Having said that a couple of single speeds did pass me on a rough climb.
It’s a great route and the organisation is excellent. I will definitely do it in the future.