Tom - Here's my experience getting boots that fit - maybe you can glean something useful from it. I started out looking to replace some old Asolo Glissades whose sole had peeled off. Looked at the NNN-BC boots: felt that they would be about like what I had had before, maybe a little less beefy. I wanted more beef, not less. Looked at a couple of Karhu 3-pin boots - Convert and Sirius, I think - found them to have a sole a little less stiff than what I had before, with uppers maybe stiffer, and the fit was not good - too high-volume for my low-volume foot (wide but flat is my affliction, and my toes are shorter than normal, which tends to confuse inexperienced boot fitters). Pretty much decided to go for the lightest plastic boots. So I went to Marmot. They had bot the Scarpa T3 and the Excursion, the two lightest. The scarpa was a little narrow for me in the forefoot, and just didn't feel right. The Garmont felt like it could work if this thermo-molding thing was for real - in other words, out of the box it would not have been right, but it wasn't way off. As I said earlier, the guy there worked hard to prep them. I'll try to describe the assembly: First, he built a custom toe cap, using a standard one as a starting point and building it up with some other stuff - moleskin, I think. Then he picked out a thin sock, and we put my orthotic inside the sock against my bare foot, and I think this was taped together so things would stay put when I stuck my foot into the liners: then he heated the liners, and stuck them into the shell, my feet went in, the boots were buckled, I stood with the toes of the boots propped up slightly so they would mold with the toes flexed a little, and I had to keep my knees bent a little as well while the magic happened. It all felt rather strange, and not really comfortable until the process was complete and I could get the whole build-up off and try them on with just a pair of socks. Seemed pretty good - definitely a change from the out-of the box fit. And time has shown that the fit is very good. I have plenty of room for my toes and a snug fit everywhere else, and my heels are held down really well.
I don't know how this compares with your experience of having your boots molded: if it's significantly different then maybe that is useful info. I also heard from the guy there that most people can't fit both Scarpa and Garmont - it's usually one or the other.
From my perspective, having had poorly fitting boots before, I would say it would be worth it to drive to Mammoth (or there may be shop in Bishop that knows their stuff) just to get a good fit. It just makes so much difference. Besides, once you're up there you've got great places to ski - or hike if you go in the summer.