Well, here's my unscientific view on this.......
I've recently done a complete step-by-step upgrade of my main desktop computer.
Original specs:
Asus Max. IV Gene-Z
i7 2600k @ 4.6GHz
16GB Corsair 2133
250GB Intel 510 SSD
HIS 6970 gpu
Current system specs:
Asus Max. V Gene
i5 3570 @ 4.4GHz
16GB Corsair 2133 (same RAM)
250GB Intel 510 SSD (same SSD)
Gigabyte 7970
Did the upgrades in steps......first, the gpu.
Second, the motherboard. After selling the Gene-Z locally, I spent maybe $25-30 for the upgrade at most (including gas cost of delivering the mb to the buyer.) I bought the Max. IV Gene-Z on sale...I tend to wait for sales on parts I want. I'm sometimes patient.
Then, I bought the 3570k as part of a MicroCenter mb/cpu combo for the $50 off the motherboard (I bought an AsRock Z77 Pro4-M for $59 with the cpu. That motherboard, along with a G620 cpu purchased at the same time for $50 from MC went into another computer build.)
Sold my 2600k to pay for the cpu/mb purchase. While I sold the 2600k cheap, it had no further use around here and I'd rather see someone use it than have it just sit in a box. (And I bought that 2600K as part of an old MC $80 off motherboard/cpu combo purchase.....sold the motherboard for $15 less than Newegg price and applied the savings to the cpu price, so paid a lot less than Newegg retail for the cpu. In the end, even at the cheap price I sold the 2600k for, I made a few bucks on it.)
So, after all is said and done, refurbished my desktop over a few months time and have a "new" computer for very few $$$$.
Is it faster? To my eye it seems a tad quicker on boot and opening apps up. The cpu does get hotter faster, but in the end, the max. temps I've been seeing aren't that much worse than the 2600k I was running at almost the same OC and with the same exact cooling solution (Corsair H100.)
Personally, if you're buying new, why buy the older tech when the newer tech is almost the same price? It is a slight bit faster, does run a tad warmer but not horrendously so as some try to allude to that it does....it doesn't. And it sure idles much cooler than the SB chip.