650ti performs much worse than 7850 in almost everything, which can also be seen from the pricetag. Clock speed is irrelevant metric when comparing between Nvidia and AMD, just like it's irrelevant when comparing between Intel and AMD. What you can use clock speed for is comparing two same cards like your options 2 and 3 which both use Radeon 7850 chip at different speeds.
Any of those cards will run WoW at high/ultra settings, you'll be limited by the processor first in raids and cities.