Well, yes, the Extreme may be very stable, but please note:
* Only 700 mm high in middle, almost no height at sides and ends
* "This shelter is not designed for UK backpacking in wet conditions"
So while I don't disagree about "If I were to camp at high camp on K2, this would be my tent", I do question whether two people, or even one person, would want to spend a couple of weeks living in this tent on a long trip. A different market!
> The most stable tents, however, use poles that cross.
I am will respectfully disagree here, provided that you compare equal-size tents. I have built and used both domes and tunnels, and for equivalent weight and space I have found the tunnel much more reliable. The poles on a dome are just so long in comparison. I have had the centre of a dome flex down to thump the sleeper inside in the tummy - but it was a 3-man dome.
> handle snow load much better than a tunnel tent because tunnel tents have larger flat areas on top
Ah ... not all tunnels have flat areas on top, and not much more than a dome anyhow. Some tunnels have a deliberate peak on top to shed the snow. Not many, I agree, but one reason for that is the expectation of a high wind where these tents get used!
There was a bit of a gale here all night.
> because of extensive use of guylines and bomber fabrics and reinforcement.
* Yes, definitely, on the guylines bit. But guylines are very light, and far more reliable than 'free-standing'.
* Yes on the need for careful design with reinforcement at the right places. Hey - this is a mountain tent after all.
* "Bomber fabrics" - not so sure. In my experience what usually goes first are the guylines (or stakes really), immediately followed (in time) by the long poles. Even silnylon will handle an awful lot of wind IF (IF) the poles don't move. But let the fabric start to flap loosely and ... trouble. If the poles collapse ...
OK, that's my experience and 2c worth.