I wear 40 jeans also. Just got a Mystery Ranch Selway with the 40+ belt. Plenty of belt left with heavy clothes on. The torso is adjustable from 17-24 inches on the new guide light mt frame. Put about 50lb. in it to get it fitted right, and it is very comfortable.
Having a 40 inch waist, and broad, thick shoulders, it gets frustrating trying to find a pack that fits.
I bought a Kuiu Venture for a day pack. Awesome pack, with great organization, but I max the waistbelt out with light clothing. The shoulder straps had to have the sternum strap down to the bottom of the straps with light clothes. I'm going to have to sell it, regrettably.
I have a Mystery Ranch Scapegoat 35 coming for a day pack. Not the organization of the Kuiu, but if it fits me, I can get around that!