So my merc got eth reapers toll and gulli face both socket with 15 ias jewels

Which option for armor is better
Forty - he hits 22 ias bp
Treachery - 75 ias bp

The main char is blizz soso, and i need the merc to kill fast cold immunes on diablo and baalruns.

I got also obedience eth gt, do you think i can get faster killspeed with obedience instead of reapers toll?

Treachery > Fort

Go with eth reapers.
Go with eth treachery.

Treachery always.

Why you ignore so easy fortitude, i think 300 ed is pretty nice combined with % deadly strike on this setup, not to mention @res, max light res (vs souls) and huge def bonus.

If your mercenary doesn't provide Might, then Fortitude is better than Treachery.
If he does, then both armors are more or less equally useful.

Obedience is a good choice too, but it lacks some leech (since your helm has none).

You use Reapers for the curse? Go treachery.
You use it for high dmg? Go forti

Eth treachery + eth reaper = best ever

doesn't matter if Treachery is eth or not, his def will be cabbage anyway
Eth forti is good because of frozen armor. I'd take treachery, Guill, Reaper

if his res is alright and u cant reach another bp with the45 extra ias of treachery i would go with forti
gulli with 15 ias ed jwl or so
eth reapers with 15 ias ed jwl or so
forti

have this on my blizz sorc in bnet
he is so strong