I dont have experience with the MM Fat Beams, theyre on my list though. Ive played other sets of DR Strings and love em
I think that you will have no problem with the length, capable of being strung up to 37 1/2 inches. I have a five string i think long necks are on it, theyre tapered, but the B string is nice and tight, and responsive. A thicker gauge will give you a fuller, tighter sound along with more stiffness imo.
As for sound, and life of the string? The sound might be a little clackity, trebly, very clean at first, but once you break them in, the sound awesome. lifewise, I practice three, four times a week for about an hour each time. I play classic rock to metal, and they last me about 3 or 4 months.