Going uphill with a full pack, I figure on 2 mph, plus add a half-hour for every 1,000' of gain. That takes into account a 5 minute break every hour, but doesn't count longer breaks for lunch, etc.
Going downhill is a bit faster, but still figuring 2 mph on average isn't bad.
Those are both for on-trail hiking. Class 2 (off-trail) is another bet, entirely, as is anything that takes you over about 12,000'. (Sorry, folks, I'm metrically-impaired)
The article had several good points, including the comments about descending on loose surfaces. USE that slide on the scree, if you can keep control, and glissade just as you would on snow. The extra 6" or so each pace shortens the trip down.
As an example, with full packs, Nathan and I spent about 5 hours going from Whitney Portal to Trail Camp, which is roughly 6 miles plus 4,000 vertical feet. That doesn't count lunch, nor the time we spent at Outpost Camp waiting for a t-storm to blow over. The next day, with only day packs, it took us the same five hours to go from Trail Camp to the summit of Whitney, about 4.5 miles plus another 2,500 vertical feet, every inch of it above 12,000'. Return from the summit to Trail Camp took about 3 hours, and the return hike from Trail Camp down to Whitney Portal the next day took a similar 3 hours (again with full packs on that stretch).
We're not particularly fast hikers, and I can still outwalk Nathan going uphill (he's 12 and I'm 50), but he matches my pace going downhill. On the way out, nobody passed us between Trail Camp and Whitney Portal, and we passed several other groups.
(By "full packs", I mean about 25% body weight for Nathan and between 25% and 33% body weight for myself. A "day pack" will be between 10% and 15% of body weight, max., and generally gets noticeably lighter since a lot of that weight is water on a dry trail like the upper part of the main Whitney trail.)
Alan Ritter, firstname.lastname@example.org