Looks like at base clock speeds it's a ~50% increase vs a 2600K. However, I have a ~20% OC so I really need to see how much the 6700K OC's. Still it's seems unlikely to be worth spending ~750$ for a new CPU, RAM, Cooler, and MB.
25% faster clock-for-clock would probably fix this in most of the games I care about, and that might be enough to get me to upgrade.