The 3570K is as good as it gets today for gaming, regardless of price.
I think it will be good for that purpose for longer than anything else you can buy today.
4-6 years might be pushing it though.
You will want a Z77 based motherboard that gives you multiplier overclocking and pcie 3.0.
I would not spend a bunch on a enthusiast motherboard.
Any Z77 motherboard will OC to about the same conservative limit.
Buy based on the number of expansion slots you need or sata ports, or whatever features you need.
Consider a smaller, cheaper M-ATX format with 4 expansion slots.
Past that, most any Z77 motherboard will do.
Some will suggest a more expensive cf/sli capable motherboard for the futute.
But I have doubts on the wisdom of that.
Today, a single card upgrade can go from your GTX560 to GTX670, and even a $1000 GTX690.
All still using your 750w psu.
Next year, we will see GTX7xx and amd 8xxx based cards that are even stronger.