Even if the X720 releases first, there's still a strong chance that it'll still be more powerful than the PS4. Sony can't afford ridiculous specs at the moment (according to some of the fine folks in Kowen's latest thread, anyway)
My prediction threads:
Wii U will sell under 40m units (made on 14th September 2012)
PS Vita will sell under 20m units (made on 30th September 2012)
Wii U will sell under 7m in 2013 - I was right