I have a 3 bow, 54" and I can stand underneath with some room to spare (I'm 5'8"). Depending on your height, you might get away with a 46". My debate on this was do I want to stand up underneath or sit down. Check the past posts out on this same subject.
Barb actually provided me with a good analogy on the issue (i.e, had something to do with bending over a chair for long periods of time I think). Thanks again for that one Barb.
Hope this helps.