Overboots are tricky for two reasons. The first is that they can be difficult to put on, and difficult is something you really want to avoid when operating at high altitude. The second reason is that overboots interfere with the fit of crampons.
Mountain Hardwear’s Absolute Zero line is built for high altitude mountaineering. These overboots have velcro almost down to the toes making them easy to fit. The closed cell foam pads are removable, so you can mess with them to get them to gracefully accept your crampons.
There are other good overboots out there such as the Forty Below Purple Haze and the Outdoor Research Brooks Ranger. They weigh about 26oz. per pair, however, compared with the Zero’s 14oz.