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Personally mate, if i was on an sb setup thats what id do. Ive been through ivybridge i5 and i7, haswell 4770k and now 4790k. The gains have been very small tbh.
This tbh, i found the 4770k at 4.2 matched my old 3770k at 4.5. The 4790k is basically a hotter running haswell chip with a higher stock turbo speed.Sensible in doing the same. There last few generations of CPU have been pretty underwhelming post Sandybridge, a few percent better IPC but don't clock any better, or worse even.
I moved from a 2500k clocked at 4.4 to sig specs (needed to as the Mrs Machine required an upgrade).
I've not seen any real difference. Save you money Jimlad and wait it out.

This tbh, i found the 4770k at 4.2 matched my old 3770k at 4.5. The 4790k is basically a hotter running haswell chip with a higher stock turbo speed.
the 2600k is more than capable still you wont NEED to upgrade it for at least another 3 years.
Look at the people still running i7 920/930's still no point in upgrading really when it comes to gaming