I am highly qualified to answer this. I had a 50D, sold it for £500, and bought a 1dMk2 (not N) for £500. My photographs improved overnight. Amazing AF, amazing depth of colour. Images just popped. Built like a tank, and really well balanced with solid lenses.
Best move I ever made. Half the number of pixels not noticeable, much better images from Mk2. Why this should be I have no idea, it just was.
Things to bear in mind. 50D much easier to use, more intuitive menu system. Mk2 requires 2 hands to do almost anything. Fiddly, though you get used to it. I use a Mk3 now and do not miss the operation of the Mk2 one little bit! 50D has a lovely screen, Mk2 compares badly. Particularly if shooting at night , be aware that the Mk2 is showing its age in terms of high ISO performance, the 50D outclasses it easily.
All that said, I think the mk2N version has a better menu, a nicer screen, and a slightly larger buffer. Still a much better camera than a 50D, even if older. Do not hesitate, you will never look back. For sports, and for the money, you can't beat it. Different league.
Rgds
Jonathan