I am another one R9 285 owner that has the exact same problems,random crashes within a fight.A few points i would like to notice:
It's not only happening with swordfight,it has crashed for me with igni alternate form quite a few times.
It is in my experience completely random,you can play for hours and not notice it or it can happen in the first fight after you load.
I think the whole 'no blur,motion blur' etc is just a placebo,i usually save before a fight and if i crash i disable all post processing effects and reload,sometimes it works,sometimes it doesnt,it's just the randomness of the crash imo.
The same applies to underclocking,i thought i found the solution because i was stuck in a quite large fight at the end of chapter 1,over a dozen crashes,but again it was crashing,no matter what options i had off,or how much underclock i was doing.
So i tried something else and well it worked,of course i am not suggesting it as a solution,but for me it worked in that particular fight which was the only one i couldnt progress even after repeating tries.I overclocked!Not by much,just 50 Mhz,but in my surprise,i finished that lengthy fight and played a few hours afterwards with no problems.
Also temperature of the GPU was monitored,it was peak 61 degrees with underclock and 66 with overclock,both quite low imo, so i dont think it is a problem related with temps.
I dont want to change OS right now to win10 that some people say it's working with new drivers etc,so i will just do the same procedure,quicksave before every fight etc,and hope that AMD pushes some new drivers soon.
Out of topic but far more serious problem imo is the 'no xp from quests' bug that has happened to me too,hope for new patch soon.