FPS Stability
All you say is pretty much normal to me. My specs are almost identical to yours. As you mentioned: it depends on how much is going on on screen. When it depends on the direction your looking in it’s tied to the render distance of that map. Sometimes the game calculates the map state if you merely look into the direction of a crowd of people. Tequatl can lag your Frames even if you are on the other side of the hill behind the laser if you just look at him, just because there are so many people.
LA is particularly bad, because it’s generally extremely high populated.
VB is wonky because of a lot of smoke and particle effects.
And WvW/World Bosses: Well… Anyone who tried spawn 1000 zombies in Minecraft at once knows what to expect.
Hope this explains a few things.
Cheers