The 470 is a nice card, and much better at $300 than $350. Nvidia has really shored up its drivers and boosted performance quickly, and Fermi is looking like a hot, power-hungry, but effective architecture. It also doesn't hurt that Crossfire doesn't scale anywhere near as well as SLI and that the 5830 is closer to the 5770 than the 5850 in performance.
The disparity in platform is telling, too, though it is hardly a surprise that the 720BE only matches the 750 stock speeds. In most CPU comparison benchmarks I've seen pitting the 965BE and 750 together, they are neck and neck (aside from a few select titles) at stock speeds, despite the nearly 800MHz difference.