Buy the PC-E 24mm. The D7000 has all the resolution you need for superb 20"x24" and larger prints. Unless you're planning to have people inspect your prints from 12" away (in which case they'll hardly even know what they're looking at), the high resolution of the D7000 is more than sufficient I think.
The D800's full resolution of 36mp is a photo retoucher's dream. Those dogs need lots and lots of pixels to push around in order to make models, products and old actors look, respectively, slimmer, better and younger while keeping everything looking real. That's what 36 mp are for IMO.
The larger the print, the great the distance at which it must be viewed for full impact. At 12.3mp several years ago, I think, we already passed the point at which more megapixels mattered for big prints.