Here is a good review for ya:
http://www.bit-tech.net/h...-i5-3570k-cpu-review/6
 
It would be a good upgrade, even better if you go with faster memory. I had a i7 950 @ 3.76GHz with 6GB of 1600MHz RAM.
 
Now I have a i5 3570K with 8GB of 2400MHz RAM and I definitely notice a difference in my games even with a GTX 580.
 
You will really need that i5 3570K if you decide to go SLI. In that first test they used a GTX 590. In this test, they use a GTX 690 with all of the high end processors so you can really see what processor holds up under full load:
http://www.bit-tech.net/h...6/amd-fx-8350-review/6
 
That's when you really see the i5 3570K shine... And they are only using 1600MHz RAM on that set-up... When I went from 1600MHz, to 2400MHz, my FPS games ran smoother and my vantage score went up 1800 points for the average.
 
As for Haswell, we might see it in June this year, but nothing is solid and they've all ready kicked back Ivy Bridge-E to Q4 of this year as well. So... If you have the patience, go for it... If not, that i5 3570K is a solid processor for the money.
 
 

It depends on what you want out of the processor... Games in general, I wouldn't be able to justify 100 dollars for such a minimal upgrade over something that can perform within 2-3% of it.
 
As for motherboards, the MSI MPOWER is what i'd choose. If you want the best, i'd get a Gigabyte UP7. 

Well... That's going to be hard to find. You will want to change your selection over to a X79 set-up with a i7 3820.
 
This motherboard would do good.
http://www.newegg.com/Pro...x?Item=N82E16813128562

On CPU-intensive applications (largely media encoding), a Sandy/Ivy generation processor at stock 3.4GHz = 3.8GHz Nehalem quad-core, so without adjustment it will equal what you had before overclocked.  
 
A casual overclock can be achieved easily raising the frequency towards 4.5GHz, equivalent to your i7-920 to 5GHz.  Many regard this as legit enough, they use overclocking as part of the decision process, even though no particular overclock is guaranteed.
 
Just so you know, in about three months a new socket will come to succeed LGA1155, LGA1150-- you might as well wait for that.  At least that new architecture will add another 6% at least making a stock 3.4GHz Haswell = 3.6GHz Ivy Bridge = 4GHz Nehalem, in CPU-intensive applications.  May not seem like much, but you can't just upgrade the Ivy Bridge as the sockets are incompatible, so you might as well wait for something worth the initial upgrade cost.
 
The upcoming Core i5-4670K is projected to occupy the same price as the current i5 K's in the lower $200.  The Z87 boards they go into will be priced like Z77's are now, for the most part.

Duarian
Edit: just read ivy bridges run hotter than sandy bridge. Not really sure what to do now honestly...

Historically, shrinks meant lower temps, but Intel changed the TIM between the die and the IHS from the fluxless solder to thermal paste for Ivy Bridge desktop mainstream, which resulted in less heat transfer and more absorption, thus warmer than expected temps.  You could go with it on the excuse of using less power (14W saved at stock, up to 50W saved overclocked), pull the IHS off yourself and change the TIM (risky, might damage the die), or wait for Haswell and see if Intel did anything different.
 
The idea did this to hurt overclocking is conceited; the decision to turn a limited overclocker (non-K) into an unlocked (K) processor is likely done after fabrication, which is why Intel kept the TIM and included the integrated GPU in the same silicon-- both of which many have little use for.
 
What are the chances Intel did this to Ivy-E and Haswell and any new debut from here on out?  We don't know, but Intel clearly did it to save money using fluxless solder yet maintaining stock operation; nothing to do with overclockability since they aren't about that. Overclockability is just a by-product of designing the processor to last a long time, it is about load cycles.