I used to tour in my alpine boots, but after painfully scrambling up a scree-field on a 14er in Colorado, I made the decision to get some AT boots. I talked to a good friend who manages the Surefoot store in Beaver Creek and he said the Radiums were the best AT boot out there.
When I first put them on, my toes felt pretty pinched. I have some serious foot problems (bunions), but have heard from others that they have the same issue. Regardless, after a bunion-punch and the heated liner fit, they felt great. By no means are they as stiff as an alpine race boot, but they felt solid enough for my hefty touring setup (K2 Hellbents + Marker Dukes).
I tried on the Tecnica Agent AT boots, which were extremely comfortable and roomy, but too soft.