Nothing, unless your CPU is reaching down throttling temperatures, which can be analyzed with either the program’s Speccy (Recommended by Anet) or CPU Z, there isn’t really much you can do other than overclock your CPU to a higher clock speed.
Word to the wise, you still won’t see that much of a boost If you decide to take the overclocking route, as mentioned before by users with I5 4690K / I7 4790Ks which despite the slightly more age, outperforms your CPU in Single Core / Multi according to several benchmarking tests and even then they have trouble stabalizing a constant 60FPS in heavy populated areas (aforementioned WvW / PvP as well.)
All you can do is either accept this flaw or move on. (Don’t take it the wrong way as I myself as a GW2 player would love to see you enjoy the game.)
The game is behind on engine tweaking thus does not utilize newer processors with multi core technology unless they decide to rewrite the engine with DX11 or more successfully with DX12 since this would be the better option for multi core processors.
Until then, that’s the games only downfall, hope this doesn’t affect your decision on staying but at the same time eases anything you might be worrying about hardware wise.
You have a great CPU / GPU.
