I, like many of you it seems, was having a lot of trouble killing Orchendor, but I found a way, and a fairly easy one at that. When you get to the dwarven centurion a little ways before him don't kill him!! Do whatever you can to get past him and run away until he loses interest. You might stumble into a batch of spiders, but keep running until you're not being chased anymore. If you want, at this point you can go back and deal with the spiders, but still keep the big guy alive. Now, once you get to Orchendor, just go up enough to get his attention, and as soon as he sees you, run away, he's fairly persistent as far as chasing goes. Sprint past the Centurion with Orchy in tow, and keep going. It's best if you can drop down into the water, but as long as you can get the centurion off you you're fine, because then the centurion will turn around and start beating on Orchendor. Just chill out and nibble on a sweetroll until you see the quest update pop up, then go loot Orchendor, and kill or avoid the centurion as you see fit.
From: CarefreeDude | #008 I admit, I had to google to know who he was. I almost said, "Just do the peryite quest and get spellbreaker"
Well, that is the only way to kill him.
It's been a while since I did that quest (on my first play through, in fact, so a long while). I was using a dual-wielding Altmer tank (LH dagger and RH sword, heavy armor), and probably just hack-n-slashed until he died.
Mr. Spock, the women on your planet are logical. That's the only planet in this galaxy that can make that claim.