My merc uses Gaze, G.Bane and the Unique Threasher. His resists are low, but that does't seem to matter, he almost nver dies. He can tank Meph for at least 30 secs before dieing.
I like the Unique Theasher with Shael because usually the moster's get decrepified, and that makes up for the lower attack speed (also helps with crown control with every thing moving sooooo slow). I'm most likely going to put a 15ias in the gaze and bane.
Toothrow was my choiche so that the merc could use the bonehew at lv 78. It also gives nice 40% OW. Rare circlets can be nice..the often spawn with leech and +str for me (even in the +13-19) range and res all.
Never considered using Guillaumes and dual Amn...but I would also have the option to go dual Shael and Tals Mask. Too bad if I'd die...I'd loose 2 Tals masks. I noticed that a Hone Sudan, 2 Shael, 1 Amn and Rattlecage with 70% CB worked wonders on NM Baal.
Maybe that with a Guillaumes face is even better than the bonehew???