I have learned MOST of his solos pretty proficiently and I can say, the two most difficult FOR ME were definitely MIA and higher. With MIA your economy picking has to be really controlled. With the licks in that one, there isnt much room for slop. With Higher, your legato has to be really even while also doing some pretty wide stretches.
But no matter what, I would say not to think of ANYTHING as difficult or easy. The best way to improve is to mentally KNOW that you can play ANYTHING, its just a matter of how much time you are willing to dedicate to any given endeavor. It’s kind of like the matrix- dont think that you can make the jump, KNOW that you can. The brain really is an amazing thing and if you go about life ASSUMING that EVERYTHING is possible, your brain has a way of just making these things happen. It’s all about willpower, preseverance, and dedication.