Infinity on eth cv or non eth thresher?

Well the title says it all, I cant find any eth thresher/giant thresher, I've only a non eth threser or an eth cv to make infinity for my trapsin merc, is that ok, or do i keep looking for eth thresher?
Edit: i socketed the thresher, got just one sock , i've now only an eth cv.

 

If you're only farming regular mobs (cows, for instance), then a non-eth polearm will do the job. But if you're going for bosses, it will take much longer to put them to sleep.
As a general rule, you should always use an eth weapon for mercs (+50% base damage), especially for fairly expensive runewords such as Infinity.
And the rest is to adjust gear for a specific IAS breakpoint that you want to achieve, while keeping an eye on other useful mods - CB, OW, etc.

 

I wouldn't sweat it, threshers are only marginally better then cvs in terms of speed, with 60 ias on merc you have 1 frame slower jab which attacks 85% of the time, and 2 frames slower normal attack. You will do most of the work anyways. Imho better to have eth weapon