For people, encountering the same issue - at least if you own a GeForce card - I can provide a HALWAY-workaround:
download the NEWEST nvidia-driver. It was released a few hours ago.
Now activate "Anti-Aliasing FXAA" and "Vertical Sync". Ingame your now deactivate Anti-Aliasing as well as V-Sync. The FXAA-support is new with the latest drivers.
The chewing-gum-like fps-drop stopped for me - my FPS seem to settle at a pretty constant 30 though. Fights now feel better because my mouse does not accidentally (ha, the irony...) hovers over loot anymore and drops my fps.
I for myself prefer it this way, until Blizzard gets their !@#$ together.