Depends on which wheat you plant and what area you farm in and if you are trying for high yeilds. Need more info from you ~ Spring wheat, here in Mn, doesn't tiller very well, in our climate and soils, so 10" or 15" wheat wouldn't yeild as well as 6in drilled or even solid seeded/equal distant seedlings and would have compitition from weeds all year.

Check this site for very usefull info on high yeild wheat production. http://www.milesnmore.com/opticrop/index.htm