your right, for gaming there is no reason to use the i7 2600k, so for a lot of people on this forum (including you) it is a waste of money. however, for those who do a lot of CAD work, major photoshop work, a lot of video encoding, etc, then the i7 2600k gives a major performance boost.
as for the motherboard, the only difference i can see between the gen3 and the standard is that two of the PCIe x16 slots (graphics card slots) are PCIe V3.0, rather than V2.x. the only way i can see it making a difference is with the next generation of graphics cards, because no graphics card on the market today is slowed down when running at x8 speeds (which it will do for crossfire)