Supposedly Garmont AT boots do have the smallest volume relative to the length, but the garmont liners are also some of the thinner heat moldable liners out there. This could be a load of bs but I was told by some folks at a local shop that Garmont teleboots have a wide last, Garmont AT boots have a narrow last and Scarpa boots are just the opposite AT-wide, tele-narrow????strange, huh?
I have a pair of Garmont Megarides and after a few trips I've given up on the Garmont liners and put my old, thicker, wrap-around tounge Raichle Thermoflex liners in the shells and they fit much better.
If you are willing to pay a little extra, you can take a tighter fitting pair of AT boots to a bootfitter shop, Jim Mates-Custom Boot Service 6500 4th Ave NW Seattle 206-297-9298 is one local option. A good ski bootfitter should be able to heat up and stretch the toebox of the shell a little to make room for your toes. Expect to pay at least $60 for this, and Jim is not good with giving out cost estimates over the phone, in my experience.
If you opt to stick with the boots you've got, you can always use a thicker pair of socks or put some shims under your footbed to take up room...but if you are already cranking the buckles down all the way, I'd really take a look at a smaller shell size and then having those shell cooked and stretched.
Unless you're thinking of using the boots for high altitude or long cold weather trips, get them tight...then just pack a pair of down booties to switch in to when you get to camp!