One thing to keep in mind is that regular pins will always set before security pins. Since this lock only has one mushroom, it means once you get a false set the lock is basically picked... just get that pin set correctly and the lock will pop open. Don't try to avoid false sets by using extra light tension... the spring return will make that a pain in the ass.
Can we see the bitting on the key, maybe with the hook you're using beside it? I don't have much experience with masters but if yours has the same profile as the #3 and the #40 then it'll be tricky to get larger hooks in there. If it has a crazy bitting then something with a sharper hook at the end would be a wise choice, but in all honesty you should be able to get around any kind of bitting master has to offer with top of keyway tension and a short hook.
I will now tell you a story. When I was first starting out, people told me about how you only need a couple of picks and I was like "no way cos this lock just won't open, I need a different pick". I actually got to the point where I gave up altogether and my picks sat away in hiding for years before I got them out again. That happened twice! I started again about a year ago, and have done a LOT of reading since then aswell as asking tons of qestions just like you're doing. Long story short, you're gonna get that lock open.
I have an abus 65/40 with a really tight keyway and a complete nightmare of a bitting; if a short hook can get around that then it'll deal with anything master can throw at you. Yes, sometimes there is the perfect pick for that one lock and it makes your job much easier. But I want you to get that short hook out, run it down the side of the key and imagine it's in the lock. If you can get at all the pins without disturbing the others against that key, then you can do it in the lock. If it doesn't look so good against the key, find the one you like and get it in there. Get it to false set, deal with it and get that bitch open.
If you're picking for an hour, take some time out and do some reading. Try different techniques, different ways of holding the pick etc. Don't let your fingers get tired either... I can remember spending up to an hour at a time with one particular lock, and my fingers were shaking. If your fingers get sore or start to shake like that, take a break.
Don't keep switching picks while working on that lock either, find one you like and stick with it. That's a mistake I made, switching picks every 10 seconds... didn't help one bit. You need to sit with one pick and work out the technique for that lock. Pay attention to what it's doing and pretty soon you'll be opening it in under a minute every time, asking yourself what all the fuss was about.