Prime95 was run for overnight (8 hours) aswell as a 1hr hour OCCT run - not exactly proof of 24/7 stability but it's good enough imo. This is compared against similar results with the MSI and P5Q deluxe. I rated the Maximus higher as, along with the ridiculous amount of BIOS tweaks available with more time and a more mature BIOS it is my belief the Maximus can at least equal the P5Q, not only that but gaming wise the maximus is already ahead of the P5Q albeit not by much.
Also overclocking on air, as I'm sure you are aware, can be heavily influenced by ambient air temps which due to the recent hot weather is limiting the possibilities. Using phase change is not realy an option as it isn't indicative of the 'average' user and wouldn't give a fair representation of the possibilities of the motherboard.
Because the P45 uses PCIE 2.0 which is double the bandwidth of PCIe 1.1 the need for 16 lanes is debatable so going for an X48 (which appears not to clock as good as P45) is not a decision that should be taken lightly. I guess it comes down to if you want every last ounce of CPU or GPU power - CPU = P45, GPU=X48 imo.