$1400 is not a good deal for a pc with dual 5770s. I think you should build your own. A GTX 570 is much faster than a pair of 5770s. Two 5770s is about the speed of a 5870, which is slower than a gtx 570 by a pretty wide margin.http://techreport.com/articles.x/19404/11
those are old benchmarks, but you'll be able to see the disparity between crossfired 5770s and a gtx 480. http://www.guru3d.com/article/geforce-gtx-570-review/12
There you can see that a gtx 570 is usually faster than a gtx 480.
If you can wait at all, I would suggest delaying your build until Sandy Bridge parts are available.