Well, you can imagine how much I used => started off with arrows and stunned him
http://www.kiya1.de/beyond/act4screens/Final60.jpgcontinued with arrows/stunning
http://www.kiya1.de/beyond/act4screens/Final20.jpglost patience and...
http://www.kiya1.de/beyond/act4screens/Final70.jpgit was tedious in this mixture - and I had even less success in sneak mode in hitting him with arrows (though needed only a few vitality potions in this. Was only puny lvl 30 though. Watching the pics from start to end => you can see how many potions I took. I required far less by only using magic.