hrmm idk about the 770 personally its around 680 performance lvl, but i can vouch for the 780..
so my pc is i5 3570k at 4.3ghz 16gb ddr3 1333 memory with several virtual drives created in ram for fast access to specific files and a 120 gb ssd

corsair 850w psu and a gtx 780/ screen is dell u2412m @ 1920x1200 and my fps varies, for titan hm 100-130 fps/ massive fates would be 30-50, like the peak hour DD fate before the bugs/ in town at mor dhona on the roof of the shacks looking at crystal and all the ppl i get around 15-40 depending on how players are there.