Can't really cast a vote of preference between the two, since I have each and like them. But the GB is likely "better" in general.
The Tsumura is on my Efco 981. Very nice bar, I really like it. Even though I heard it wasn't of very high quality, I have no complaints. It is a myth that the Japanese are incapable of quality metallurgy. A simple history lesson in their edged weapons or industial arts would prove that.
I have a super-deluxe titanium GB bar from Jeff Sikkema which is excellent. It is the same bar he has shown on his 7900, but mine is for my Stihls over 70cc. But I also have some older mid-level GBs which are no big deal.
It would seem that the potential for a better bar on the high-end goes to GB.