Cheers for the comments. The general opinion suggests that I stick with Draft I until Eskdalemuir, but figure out a better route from Eskdalemuir to Carlisle. I'll take a look at the options, tho they are probably limited to the B723 to Lockerbie or the B709/A7 to Langholm / Longtown.
Not sure how often you'll want to stop to refuel but the only shops you'll pass on this route are in Haddington, Innerleithen and Carlisle.
To be honest, I hadn't considered places to grab supplies, but it's probably something worth thinking about. I'll be doing this ride on a Sunday, so that'll probably making getting food even more tricky.