FWIW (I'm not sure it's worth anything, but it's a little interesting), I'm 6'4", and one of my 64cm bikes came with 42cm bars. I rode with them for three or four years and felt fine. Then I ordered a supercheap set of 50cm (yes, 50) bars from Nashbar for my singlespeed, and when they came, i liked them so much I ordered another pair for my main bike. I really like the extra width. It's not easy or cheap to try a range of widths before you decide, unless you're cozy with a bike shop owner, but if you can work out a way to test-ride a bike with wider bars, you may be suprised. Anything narrower than about 46 feels cramped to me now.