I am looking for a mountaineering boot that can serve as my only boot essentially. I live in Colorado and climb year round. I want something that will be decent on rock, but also warm enough for winter. Some people I have talked to recommend this boot as able to get through anything in the lower 48, others say not enough insulation for winter mountaineering.

Any help is greatly appreciated.

Yes, it will be fine. What you want to do is just get some quality overboots or boot covers. 40 Below has a great selection of lightweights. Try Whittaker Mountaineering. I've also used Pearl Izumi cycling shoe covers because they are cheaper. But if you do that, make sure you get a couple sizes too large and TRY THEM ON because cycling shoe cover sizes are uber-tight. You won't be able to get them on and off in the cold unless you can get them on and off easily in the store. I like cycling shoe covers though because they are only ankle-high, and sometimes that's what I want. I also don't feel so bad about wrecking a pair.

If you have reasonably warm feet, this is great for winter day climbing in CO, but may be too cold for expedition or multi-day use.