In reply to sparkass:
The quality varies with the horizontal bedding in the rock - it can go from bomber to wet talc in a few inches, repeatedly. Not done Big John but I think the rock is worse lower down (or buried under steep grass) and better higher up. Probably still all XS due to the lichen, damp and birds though - Longhope to the right is much cleaner on the last few pitches.
Mucklehouse wall has some sandy sections and some very clean sections, but the top quarter is sandstone as good as you get anywhere.
I doubt very much that if you're up to climbing Big John or Mucklehouse wall, the best route on the Old Man for you will be the original. We did For a few dollars more on the north face, which was great. The South face and bounding aretes looked good too.