Zoran, I think you’re referring to the old UK Scarpa sizes, where a size 8 UK was really a 9 US? (My wife’s Scarpa Magics came with four sizes: UK, US, Mondo, and Euro!) Scarpa is emphasizing its mondo sizes this year, so that should eliminate some confusion (unless of course the euro sizes are still stamped on the shells, ugh).
Re fit, since Zoran noted that some Scarpa mountaineering boots fit differently, you should be aware that the Scarpa Denali series (both the current TT, the older XT, and previous four-buckle red version and the original three-buckle maroon version) use a lower shell that is significantly different than the Matrix and its brethren (i.e., older Laser, women’s Magic, and various economy models, mainly found in Europe, although one is finally being imported here this season). Ditto for the Garmont Adrenalin vs. other Garmont models. And ditto for Dynafit 700 (and economy 500, as well as older All Terrain) vs. the TLT4Pro and variants. (Unclear whether the fit on the new Aero will be like the TLT4Pro, or something else altogether.)
Another important factor is that the thermo liners (made by Intuition) in Scarpa and Dynafit expand when heated. So any spots that fit a bit loose will be significantly tighter when the liner is molded. (Although coming for a race background, filling shell voids with mushy liner foam is not exactly optimal, but I don’t care about this in the backcountry.) By contrast, the Garmont G-Fit liners are much more thin and dense - so if the shell fits you well, you’ll get a better fit from a Garmont, although mainly people for whom Garmont shell doesn’t fit them complain of sloppy fits. (I’m unclear on what kind of thermo liner Lowa is using in the Struktura Light.)
Besides fit, you should decide whether this boot is going to used for lift-served days, or exclusively backcountry days (and if so whether you want to do long tours, or more yo-yo turn-oriented outings), or for some combi days (i.e., ski half a day lift-served, then head out the access gates). Mainly AT boots emphasize different aspects of skiing. Yet another factor is whether you might to get Dynafit bindings at some point, which would eliminate the Scarpa Denali, Garmont Adrenalin (and G-Ride, but the MegaRide is very similar), and Lowa.
Assuming that you’re getting starting with Diamirs or Naxos, you can start out just using your alpine downhill boots at first, and see what your touring partners are using. (I recently bought a road bike after mtn biking for many yrs, and although I’m happy with the results of all the research I did beforehand, you certainly learn even more once you’re actually out riding with other people.)
Okay, gotta head out now for the last day of my three-day biz trip here, then I might not be checking e-mail much over the next four days while I visit my brother. Quite the fortunate coincidence that the biz trip is in LA and my brother lives in Tahoe which means our hiking & biking plans for the next four days have been replaced by . . .