Joris - from the information I can find, the reason the B29 was not used in European theatre was that in December 1943 (the maiden flight was Sep 42) it was decided to send the B29s to the Pacific instead of Europe (as presumably originally intended), where their longer range could be used to greater advantage - given the long distances over water needed to reach targets.
One cannot help but wonder what effect their use in Europe might have had on the war given their carrying capacity compared with B24s and B17s.
It's not that easy to compare payloads - some figures I've found are B29 max. payload 20,000lbs, B17 max. payload 17,600lbs but typically 4,500 - 8,000lbs of bombs depending on distance to target, so presumably quoted max. payload includes fuel?
For a given distance I'd have expected the B29 to be carrying a lot more payload than a B17. Over to the experts?