Well i done some testing.
It's MF barb for sure, max warcry and find potion + grim ward. I was pretty happy with him, but andy/meph/diablo runs were too bad. So i tested a bit (still haven't try out CoH because usually everything stunned and can't really hit my merc, so no shatter at all)
So i checked out throw barb build with warshrike+lacerator, played for a few hours but really not my thing. I like cry much more, because i love sorc and this build is almost same to frost nova :D
Merc stays with Insight in eth Giant Thresher. Usual boss packs are dead in 1 second because wc is around 2.5k damage +105 fcr, phys immune skip is really best way, not to waste time on them.
And to do normal speed (like 30 sec) boss runs all you need is 2x lacerator on swap, that's all. It procs when misses, and gives decent damage boost to do them fast. Not as fast as sorc, but pretty ok.
Thank you ppl for all your answers, it helped alot :)
Dependent on your skill setup, maybe 1 base point to Berserk for Phys Immune, this is what the old cryers used to use.
D2:R