Hey peeps, I just need to know quickly before I enter a new raid, if a fast offhand is necessary and is it a huge dps increase? I mean, a dagger compared to fist weapon in offhand fx
That's pretty much the jist of it. Take your highest dps slow weapon, put that in your main hand, then among all the remaining weapons, put the highest dps of those in your offhand (regardless of type).
If you can use killing spree optimally, it's usually best to use a slow off hand. But the difference in dps is minor, so generally the highest dps offhand is best.