1D AF is much better, and 1D will survive much harsher conditions (weather sealed lens needed). I would expect nothing less than perfect A3 printouts from it.
50D has a lovely super saturated screen, light weight, 'modern' technology, and shed loads of mp for heavy cropping (if in focus, and not too noisy)
i.e. 1D for pro jobs and 50D for casual snapping.