TaylorguillemetteI had the same question. I got mixed answers (here and on reddit/r/ultralight). More than not said you're better to size regular. I also emailed Granite Gear themeslves and asked them and their response was:
You would probably want to go with the Regular frame then. Whenever we have someone on the edge between two sizes, we find its better to go with the shorter size, since if its too long its can bend and bow on you. The pack body itself is the same size, so you don’t lose anything.