Personally, I think the 'uniformity' of bo is just useful for a class situation; one should train with different lengths, weights, woods, etc. and train with the bo one feels most 'comfortable' with. If you think about it, if Okinawans were using 6 ft staff decades ago...that would probably translate to at least at 7 ft staff for you. But it's very hard to find someone with a lathe that makes anything larger than 6 ft...or affordable.