femaledwarf is giving me wacky advice.

[:1]I was planning on buying the Batwing Cloak to replace the Cloak of the banshee Queen.
I went to FD to see how big an upgrade it would be. It said it would be DPS loss of around 60.
How?? +75 Agility (with +40 gem and +10 socket bonus) +33 Crit and -11 Haste.
I really don't understand how I could lose DPS.

Sometimes FDH will over evaluate haste.
Well that was MM spec. SV spec is was +364 DPS increase..
SV uses haste to get your Cobra Shot to 1.66 seconds, every thing else is DPS increase. MM uses Haste for SS and Aim shot.
Without seeing your saved settings it's sometimes hard to tell, but usually when you get a wacky result like that it's because something you're changing is creating an inferior shot pattern (which is likely not the shot pattern you'd use in an actual fight so the item is no doubt still an upgrade), so you're replacing some good shots with bad ones in the simulation. If you send me your saved setting link I can see the issue in more detail, or you can look at the two results side by side and see what's going on with your shot counts (or occasionally it's a wild hunt uptime issue).

Could you have maybe forgotten to have an enchant on the cloak?