I wear a 28.5 alpine boot that is blown out, ground, punched and the works to fit my size 12 foot. For the Garmont Adrenalin I have a 29.5 which is just a bit on the generous side for fit, but I have used it in rock scrabbling, walking, climbing as well as skiing. It might have been possible to get into the 28.5 Adrenalin with some extra stretching in the liner toe, but for the way I use that boot the extra room is fine. As the liner packed, I added a better footbet and Bontex shims to take up any room and still have good performance. Fit is really hard to judge on this boot if you do it with the liner in the boot. Remove the liner and check the shell fit. You want a 1-1.5 cm fit ideally. I would be reluctant to go tighter due to the cushy thermo-fit liner, and need for toe-room. Much looser, and the boot will get sloppy. Fitting with the liner will feel very tight (uncomfortable) until the liner is heat molded. If it feels great before molding, its too big.
Oh, you're buying online. Here is the Garmont sizing chart. Good luck! When in doubt, it fits best if you are in the top-half (right side) of the next smaller size, or the bottom (left side) of larger size. Don't go for the large end of the size range. Based on your description you are 27.5 for more performance fit, and 28 for comfort.