Great boot for Rainier
This is a great boot. I just finished an August ascent of Rainier and after 4 days of climbing I only had a 1.0 cm blister on the top of my left 4th toe. Everything else was great. I also use these for hiking in the White Mtns in all 4 seasons. I did hike 15-20 miles in them before the climb to break them in, but it was quite easy.
I typically wear a liner with a smartwool or thor-lo hiking weight sock over it. The built in gaiters are really nice for when you don't want to have to wear full gaiters. The eVent stayed completely dry and I really didn't have any issues with the ventilation.
I have been using the BD sabretooth pro's with this and I got a great fit. I attached them really tight and did not have to adjust them a single time throughout my climb.
All in all, if you are looking for a great mountaineering boot that can do double duty as a very supportive hiking boot, then I would absolutely look into these.
Size wise- I am a 10.5 to 11 with a thin foot and high arches. I swapped the insoles for orange superfeet to get more arch support. The 11 fits great with a liner and a hiking sock as well as the added volume of the insole. I would recommend these for thinner feet, but there is plenty of room in the toebox. Order approximately 1/2 size larger than you normal shoe.