The BB spindle length has to do with getting the proper chain line. If you want a wider Q factor you need to look at the crankset and try to find one with a wider Q. I think the XD2 has a Q factor of 165 mm, which is probably sort of a medium number today. Smurf Hunter's comment is a good one - Q factor is about getting your pedals to a width that is efficient and comfortable for you, not necessarily about height or leg length.