Your longevity is going to depend on your GPU and not so much your CPU. A 3770K will be a fine gaming processor for 5 years to come just like a Core 2 Quad Q6600 from 2006 is still a viable gaming proc now when paired with a powerful video card. Hell you can still have a capable gaming rig with a Core 2 Duo E6600 if you paired it with a fast GPU! However a video card from 2006 or even 2008 isnt going to be even entry level by todays standards.
That rig I listed for you will be playing games on max settings for 3 years easy and when those GTX670's run out of steam, just drop a pair of GTX870's in there and youll be set again. Games arent becoming more and more CPU intensive because theyre all having to be developed to the lowest common denominator as in consoles. That 3930K is not a better gaming processor than a 3770K. Its last generation architecture (Sandy Bridge) with 2 more cores basically. The 3770K is the fastest per core and since games still barely use more than 2 cores, there is no benefit in paying a lot extra for 2 extra cores with SB-E.
OK just one question why then is every test rig that I have seen using the 3930K or the 3960X. Secondly I would put good money on the fact that with in 3 - 4 years hex cores are being used by games.