Hi Robz,
I did it this year and doing it again next year with a group of friends. Everything stated above is correct and you really need to be able to put in that 150-160bpm stuff (or mostly just under threshold power) for 90 minutes or so. Looking at the mountains next year, i’m not sure it will be quite as brutal as this year’s although it’s still a huge amount of climbing. I would say the most important thing is to learn to hydrate and get food in you early and use proper electrolyte-based drinks.
The last 1/3 of the route was just bodies everywhere, people hiding under trees, collapsed, voming. There was a single reason for this: the heat. To beat that requires you to both be fit enough to do the course, which is all about the hills and total time on the bike as you get huge breaks on the downs, plus properly hydrating ie. 1 750ml bottle or so depending on your body weight of electrolyte fluid per hour. Plus the snacks they provide are a bit useless for electrolytes apart from the bananas, consisting mostly of purely sugary things, so I would definitely recommend supplementing your own gels into the mix as they will also give you electrolytes and sugar in an easily digestible format.
Don’t want to sound like i’m forecasting doom either as the elation on reaching the end was incredible! But I almost collapsed on the way down from the col d’Izoard and had to stop for 15 minutes and drink a lot of fluid, despite having already finished the thing! Entirely doable with good training and practicing nutrition but huge numbers of people didn’t finish and their disappointment was obvious. PM me if you want to discuss anything further.
Personally I am trying to mix up Enduro riding and road riding so I know how it is. I’m ending up a bit divided between road and mtb each week as there is some cross-over but entirely different types of intensity. But sod it, they are both keeping me fit which is supposedly why I do it ;)