I believe the 5870's are going to be restocked in the next few days, so if you can hold off till then, I definitely suggest getting a 5870. More room for future upgrade, and definitely no worries about the PSU for now.
I don't see any cpu cooling though. The CM 690 has a decent size for a mid-tower, so air-cooling should be good, but since you are overclocking and having crossfire (if you are still getting the 4870's) I suggest some cpu cooling. With your current spending I think you can still squeeze in something like a scythe mugen 2. Your choice.