In terms of pure performance, the 280x CFX might be a bit better than the 970, but you'll also have all of the problems multi card setups have. Stutter (sometimes), higher power consumption/heat, and if there isn't a profile for a game, it won't work. So I'd take a 970 over two 280x's.
The CPU in that build is an APU. I'd rather just build my own with a better CPU even if that meant a less powerful GPU configuration.