Battery life of the D4 battery is less than that of the D3, but it's not terrible.
The XQD is much faster than CF - XQD is NOT CF. Nikon won't replace the XQD slot, I doubt anyone else will do it either.
If you're not comfortable with 12mp, you probably won't be comfortable with 16mp either. It may sound like it's 33% better, but it's really only about 15% better - the D4 provides files 4900x3200, compare with about 4200x2900. Of course 24mp isn't that much better either - but it's more than 16mp. On the other hand, even the 12mp should be able to make a pretty big print. What's your definition of "big?" How are you producing the prints?
My guess is that $150 invested in post processing software will make you more large prints than a D4.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!