I think it would be interesting to see how much if at all the pros actually change front rings when running 2X in cross. Id be willing to be most of them throw it in the big ring and never shift down for most races. I have heard of some running 44/38 up front. I think That gearing would keep chain tension in the small ring better. My first season of racing I had a 46/34 up front. The chain drop was really only a problem if i ever went to the 34 for a hill or really deep mud. Since the rear derailler wasnt as stretched it would allow the chain to bounce more and sometimes come off.