Stock for stock, the 980x will genuinly whip the 920 because of the extra clock speed and extra cache. However, clock for clock (say both are at a moderate OC of 4.2ghz or so) the 980x will only be better at extra CPU tasks like rendering/encoding....and I extremely doubt it will be ''triple the price'' worth it. Once the price tag of the 980x comes down to a reasonable level, like under $500 atleast, it may be worth it. But that won't happen for probably a year. The I7 920 is extreme overkill for 95% of tasks. When overclocked, nothing is going to be slow no matter what you are doing.
Oh and the 975 is a complete waste of money, no sense in buying a quad for the same price as the hex core with more cache and 32nm.