The OP was essentially asking to compare the D600 resolution in DX crop mode to D300.
I answered assuming that he was trying to compare D600 to D300 performance, in a case where he had to crop deeper than DX. This is typically done when you need greater focal length, despite already using the longest practical lens. I may have extrapolated a bit, but it turns out that's exactly the situation he was trying to understand.
Your post specified a landscape scene, which is typically not focal-length limited, and if done correctly, doesn't require a crop, so it's not at all related to the question he was asking.
Despite some people telling him it doesn't matter, it looks like I understood the problem he was trying to ask, and helped to answer it. Anyway I have trouble imagining how 10.3MP is greater than 12.3MP in any context.
*edit* You are correct, that Paul didn't exactly phrase his question in that way. I guess I did some reading between the lines, since I didn't really believe that he was asking if 12MP was greater resolution than 24MP.