It is a fantastic camera, I can't say enough good things about it. My guess is that if you get it, your 5D2 will see a lot less use.
I use my 5D2 99.999% of the time. I only use the 1D3 for sports/action or when I feel bad that I am not using it. It's ALMOST not worth me having anymore, almost. I still really need it for shooting my friend's taekwondo and MMA fights. If only the 5D3 was 8fps, alas 



Lots of Bodies & Glass....
