As stated, the i5-2500k is better for games. It is 200MHz slower than the i7-2700k, but it is also $150 less expensive. Is 200MHz worth the extra $150? I'll let you decide...
The Sandy Bridge-E is actually meant for the enthusiast market. I'm not sure if the price / performance ratio will be worth it for a gaming PC. We'll have to wait for some benchmarks.
Ivy Bridge is the CPU to wait for; at least for the vast majority of people.