5D 2 still will retain ~ 22MP... won't go for that super dense sensor that is the D800...
I'd say, DO NOT get the 5D 2. Coming from a Nikon D300 to a 5D Mark 2, 50% of my shots are in focus (well, perfect focus) as opposed to 80-90% of my Nikon D300. I have the 24-70 f/2.8, 17-40L, 70-200 f/2.8L IS version 2, and it just seems that the Mark 2 struggles with AF. Mark 3 I hear, will be fully weather sealed, 61 pt AF.
They really worked on the AF with the MK3... which is most important to me.