ok so I understand that boots like the LS Mons, Millet everest, Phantom 8000 and the kayland 8001 are the staple for High altitude. But what if you are not going above 8000m, or even 6000m?...but thats all you have.

Me and my roomate are going to AK for a couple of weeks in May. We were having a conversation about equipment and rolled onto the topic of boots. He previously climbed Cho Oyu and bought a pair of kayland 8001's. Everything other time he has rented boots through the guide company. However this time we are not going with a guide company and he is set on just wearing his Kaylands cause he doesnt want to buy another pair of double boots. So what is going to be the downside to this. I have never worn something like that before but is it going to be in his benefit to just get another pair, or will it be alright.

he seems to think he'll be fine. but I also dont want to be 8 days in and have his boot situation go south and have to cut the trip short.

Thoughts, opinions, spray, advice?

I cant talk about Denali ( I haven't been there) but there are many other boots out there in the range you are alluding to in your opening sentence:

Scarpa Guide 6000
LS, Baruntse, Spantik, Nuptse, Batura Evo?
Lowa Expedition 6000
Millet Shivling (at least in Kathmandu)
Mammut Mamook
Koflach's
Boreal Kangri, G1

A good selection can be seen at http://www.mtntools.com/cat/alpineice/boots/04doubleboots.html

I've worn bots "too warm" for the conditions (think Koflach Arctis Expe at 25F and sunny) and the only downsides I have seen are the extra weight of the boot and the fact that my feet sweat more. That said, due to the extra insulation I have not had my feet get cold due to the extra moisture. Change socks and dry your feet.

You don't specifically say that you're headed to Denali but I guess that's what we're all assuming. If thats the case I think the Kaylands will be fine. Keep in mind that Denali is a cold mountain, much colder than peaks of equivalent height in the Himalaya.

The boots will be a bit warm low on the mountain but higher up your mate will be glad for the extra warmth. I climbed Denali as part of a group of four several years ago and three of us had high altitude boots and didn't regret it. Yes, our feet may have been a bit warm low down but certainly not any problems that even remotely threatened the trip. The fourth had a pair of Koflachs and used overboots on summit day.

If I didn't already own high altitude boots and were going to purchase boots just for this trip I would most likely go with a boot like radson mentions in his post and take overboots for when conditions warrant but if I already owned the Kaylands that's what I'd take. I've never heard of having to turn around because of warm feet!!

I saw quite a few climbers wearing LS Oly Mons and similar high altitude boots on Denali.

I can only say good words for what I've used - the Bestard Top Alpine Pro double boot. They give it to be good for up to 7k meters with a good overboot

What are you actually climbing? If you're planning a "couple weeks" it's probably not Denali - just how low are this/these peak(s)?

Also, what kind of climbing? Kaylands would be a liability on Ham and Eggs, not so much on a slog.