It takes two hits.
On Master my level 27 Nord, with 300 health, and full set of Exquisite Steel Plate armor, died in one hit from a Bandit Chief.
My conclusion from experimenting with Master is that you need to completely avoid any hits from any higher level enemy. That doesn't quite seem realistic.
you should try to weaken the strong foes from far way, then use strong fire magic to knock (or ice to slow him down) slitghly, then when he's down/slow, use something strong (stong close combat or the stronges arrows), repeat it few times, then run a bit, till you have a small distance or an "hight" advantage (the enviroment IS MADE for such fights and runs, and cover taking ect), then use arrows again, when he get's to close again use fire or ice magic knock him down a bit or slow him down (or even us dragon words)..
the fight is tough, but it's complex and a mixture of fighting, tactics, running ect. and very intens. (and not just "swing away and he'll die first or I will die first")....
ok, if the foe can really kill u with 1-2 blows, then u have to keep the distance... then run!!! (run around trees and stones ect,. it will slow done your foe)....till you have an advantage, find help or u lost him (but stealth hiting im from far, then hitting im few more times, till he gets close, then starting "that tactic" could work)..,
even just "running" away and surviving super powerful foes is intens; after playing Master after a while, u get the "survival" feeling and gameplay mechanics better
at first, it will only feel like "just use more meds, and waste more arrows", but it more than that
I love fighting with bears, but only if there's enough "enviroment" to use..(as cover, as high foot standing, as run way obstructions ect.), they can kill me fast, and they take a lot of hits (nice long intens fights), but they can^t "shoot" and they stop here and there (they're not that fast, if you can zigzag around obstructions/ hurdles)
just setting eyes on a bear takes your breath way on master (dont panic! what next!?)
foes that can shoot are ok, if they dont come running at you, ...like archers, they give cool (long) duels,..... otherwise foes that charge and shoot are hard..
(what can kill me the most, besides overstrong foes, is clicking the left stick by accident, especially when in panic)
sorry for my spelling

... these "tatics" are probably nothing new and uesd on normal/adept too, but they're used more often and feel more intens on expert/master
(once you've hunted and defeated your first bear on master, you wont want to go back to adept)