I've used a Mystery Ranch BDSB, now the G7000, for fifteen years, and for fifteen years before that I used a Dana-designed and made Dana Design Terraplane. Best packs of all time for weight transfer. They are certainly not light but when you are carrying 60+ lb they can't be beat.
There was no frame choice when I bought my BDSB, but I think I have what's now called the Guide frame. The NICE frame (NICE is a military acronym for something) is used by itself for unusually shaped loads - mortars, ammunition, a hunter's carcass, fire-fighting equipment, etc. Call MR and inquire, but I'd say go with the guide frame.