Today I snagged an older version used (in pristine condition) for a hundred bucks. It was manufactured in Japan, my version was purchased about 8 months ago from B & H for $200 and was made in Vietnam.
So, an interesting comparison . . .
I'd say that the differences between models is tiny, there are probably versions made in Vietnam better than those made in Japan, and vice versa. In my case:
My Japenese version is a minute amount sharper at F1.4 and F2. By F 2.8 they are almost indistinguishable, though again, if I had to point to one, I'd say the Japanese is sharper. By F4, it switches over to the Vietnamese version.
I wouldn't be hesitant to buy one over the other . . .
Vietnames, F1.4
Japanese, F1.4
Vietnamese F2.0
Japanese F2.0
F4's in next post.