Quote from Lumis
I had enchantress up at 6,9k damage with gear that had as much int and vit as possible. Just search for cheap int + vit rings, necks and such. The weapon was 1,2k dps 2h axe with 200 int. I did however find the damage pretty measly anyway, so now she has only int + mf or vit + mf gear on her. Don't neglect her vit, since when she's down, she's not buffing you either.
Followers gain 250% or so benefit from raw stats, so int is propably the most effective way of getting the damage high. There are at least couple follower dps calculators mentioned around this site though, so you can always check them out as well.
When the enchatress is down you lose the attack speed increase, the armour buff stays though.
OT: yeah just go for int, vit, and MF