With +2-4 dmg rings remember that faster weapons will give you more dps than slower weapons (even if the faster weapons are lower dps). I've tested this and it's not normalized.
I can hit 80+ dps on my witch doctor and 5 soul harvest stacks with only a 14dps dagger, +2-4dmg/mf rings, and a +1-2 dmg offhand and the rest MF gear.
Demon hunters can get rather high as well since it's far easier to get ~17 dps one handed crossbows and those are fairly fast weapons so the the +dmg rings scale really well with those as well.
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I can hit 80+ dps on my witch doctor and 5 soul harvest stacks with only a 14dps dagger, +2-4dmg/mf rings, and a +1-2 dmg offhand and the rest MF gear.
Demon hunters can get rather high as well since it's far easier to get ~17 dps one handed crossbows and those are fairly fast weapons so the the +dmg rings scale really well with those as well.