Well, until the next opportunity presents itself, consider that the 5D3 seems to have a major advantage that I had not remembered seeing mentioned in print: the area at the base of the hot shoe mount is shaped to accomodate the increased weather sealing around the mounting foot of the 580EX II flashguns. (Presumably, the 600EX-RT has this same weather seal; I am not sure about the 430EX II.) I noticed this when examining a 5D3 at a local camera store. This is a feature that has trickled-down from the 1D series, that outdoor photographers, who use flash, should consider. If I recall correctly, the 5D3 also has better gasketing, overall, than the 5D2.
The chorus of 5D2-owning photographers wishing for better AF was also a factor. Though I find the AF of a 5D1 to be quite good, for most of my shooting, the 7D is notably better in some conditions, so that is another reason to favor the 5D3 over the 5D2. (As I understand it, the AF of the 5D1 and 5D2 are very similar, of not the same.) While the 5D3 is not marketed as a camera for shooting action, it is probably better than the 5D Marks I and II.
The very attractive prices of new and pre-owned 5D2 cameras certainly had me considering the purchase of a 5D2, rather than skipping the second generation, as I had planned, but now I am back on-course toward a 5D3, or perhaps a pre-owned 1D Mark IV.
Canon 7D2/7D/5D/40D/1D2N/M3; Nikon F6/D700/FM3A/1Dx/Coolpix A; Canon 40mm 2.8 STM, 135L, 50L, 35L, 50mm 1.8 I, 100mm 2.8L Macro, 10-22mm EF-S, 400mm 5.6L, 16-35mm 2.8L II; Nikkor 50mm 1.2 AI-S, 50mm 1.4G, 50mm 1.8D, 16mm 2.8D Fisheye, 180mm 2.8D, 100-300mm 5.6 AI-S, 45mm 2.8 AI-P, 14-24mm 2.8G, 24-70mm 2.8G, Micro-Nikkor 60/2.8G; Voigtlander 90mm f/3.5 SL II, Zeiss ZF.2 2/135 APO