I find most shropshire races are far tougher than expected to the uninitiated. It is not so much the length of the clmbs but the steepness coupled with the fact that they are largely on grass. The Long Mynd Valleys being at beginning of Feb is always cold which knocks it up a mark or 2 on the toughometer IMO.
Whether it is harder than some of the classic Lakes ALs is another question though. I personally doubt it but again so much is weather dependent.
Of course what you would consider the hardest is basically a reflection of your own weaknesses. I'm crap at long slow gradual inclines - much prefer steep ascents and descents - so would find these type of races the hardest even though I doubt any would figure in anyone elses top 10.....