I don't think I agree with Eric. If we're downsizing to 1200 pixels, you're printing, well, 1200 pixels. There's 1200 pixels worth of information there. Fine details that may have been captured at either native resolution will be lost. If you resize down to 1200 pixels (or anything smaller than the lesser of the two originals) you'll be losing data and I don't think the difference will be significant. Sometimes this is good, though: that's why a d800 downsized to 12mp has less noise than you'd expect. The noise "detail" is lost.
Now if you crop to those sizes, that would be a very different story. But you don't get the same pictorial result, that way.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!