I would guess the only reason this might be an issue is if you go the hard-core route and setup a multibox system that includes moving primary controls to a secondary character when your main dies. (and I mean FULL control. Anyone can still pass targets and keep DPSing when their main dies)

Otherwise, the only use I have for my secondary monitors is for mousing over to do NPC talks, inventory management, trades, etc. None of which require a low ms rating.

I'd go for the cheapies. (that's a word right?)

Boom