When I was at college in the mid 80s I went to stay with a mate in Nelson for the weekend and his dad was riding the 3 Peaks so we went to watch. I had, quite literally, never seen anything like it and the idea that I would someday take part seemed ridiculous, farcical even. But in 2009, 20 odd years later, I found myself on the start line. A great event that really deserves it's status on many cyclist's 'to do' lists (I would have had another go in 2010 but it clashed with OWMTBC).
How hard do you rate it? Comparable to anything else you've done? Did you enjoy it?
That's a tricky one to answer I guess depending on whether you want a time or are competing just to finish. As above, Superstrong Geoff has multiple very high up finishes so is the chap to speak to for racing advice but I can offer something from my 'get round' approach.
I used a bike I'd had for a year. I used Schwalbe Landcruisers at 80 psi, the generally recommended tyre even if pressure a bit high. I had no mishaps at all. To be honest gear choice is probably irrelevant due to the steepness of the climbs but for what it is worth I used a compact chainset and a biggish cassette and the only modification for the event was to add some pipe lagging at the top tube/seat tube junction. From photos and the 3 Peaks forum this seems a sound approach and certainly makes the carrying a bit more comfortable which leads to...
I didn't do anything specific but was running and racing cross country at the time so was fairly accustomed to going up longish hills on foot. I would recommend walking/running up hills. I only practiced carrying a bike a few times which was probably foolhardy but I was ok on the day. Do be prepared to carry as you will have to on each of the ascents, probably for some time even if you are a very strong rider.
On the day
I don't usually have a Camelback but needing water and also to carry a waterproof jacket I decided to go with one rather than have a bottle bounce out. In 2009 the conditions were generally dry although Ingleborough and Pen-y-ghent were in cloud and the descent of Whernside was over greasy flagstones even if they were not actually wet. I'm guessing conditions have a serious impact but if you're aiming to finish then steady is the order of the day (and the start is FAST! I was miles back but still got held up on the first climb which was by far the steepest.).
So how fit do you need to be to get round?
I don't think you have to be seriously fit to finish but you do need to be able to keep plugging away over several hours; I managed to get round despite my aversion to riding downhill whenever it can be avoided. I can't really compare it to other events as it is genuinely unique, but in general I didn't find it any more or less tiring than a sportive ridden with a degree of determination. Aiming for a time may well be another thing though.
Perhaps the best I can say about the 3 Peaks is that I plan to have another go. And with so many 'must do's around, there aren't many events I'd say that about. I seriously doubt that you will be disappointed.