As above - things look compatible.
One thing to note is that unless you are doing a very large amount of multi-tasking, etc... then a 2500K will do just as well for gaming as a 2600k - at least until games make use of more than 4 threads/cores.
In most cases, the i5-2500k is a better buy. It doesn't have hyperthreading, has 2MB less L3 cache, and stock speed is 100Mhz slower. But it's $100 cheaper and if you're primarily gaming, you probably won't notice a difference.
4x2GB of RAM doesn't make sense. Get 2x4GB instead.
As far as playing all new games on highest settings with a single 6870, no. But you should get high settings on many new games (depending on your monitor resolution). If that motherboard has 2 PCI x16 slots running at x8, you can use the $100 you saved on your cpu to go towards another 6870 for crossfire. Then you'd be able to play most games at highest settings.
I would advise a more powerful graphics solution (dual 6870's, a 6950, or even a 6970) and a core i5 2500k. As hapkido said, the gaming performance between the 2500k and the 2600k is not considerably different, and the $100 saved would go to better use in the graphics department from a gaming perspective.
Take a look at Tom's best graphics cards for the money and find a price point that you're comfortable with because I think you would be happier with a better graphics card if you want to play on the highest settings.