Hi Panoramix!
Whilst I found MC tough, and had a bit of a sense of humour failure on day 3, MP for me was harder. Day 1 wasn't too bad, though the Hardknott and Wrynose section is testing. Day 2 was brutal in the morning and very long. Day 3 was a delightful spin out to the East coast and then a saw-tooth profile of steep gradients for a while. Day 4 was easy and fast. I had a lot less sleep on MP, and more physical issues (though some of those may have been down to being a bit less fit thislast year).
The >50% DNF rate should inform you about how tough this was. But do take into account the tweaks that Andy is making to the route for 2017.
Lots of the hills are more like devil's staircase in gradient than pen y pass, and I wouldn't be inclined to compare the ride to any section of LEL at all.