I dunno. If the Version III of the 1.4 TC is 10 on a scale of 1-10, I'm sure the Version II would be 9.8 or 9.9. And even if it's 9.5, would you be able to see the difference?
With some lenses and some uses, yes. One of the factors that also comes into play is focusing speed. When I purchased my 2.0, I tried two versions, and one of them hunted noticeably more than the other.
I believe that you can get good copies of each version, but the chances of getting a good performer increases with the latter versions.
As far as which to get, either the 1.4 or the 1.7, the 70-200 2.8 AF-s can handle either one of them. You'll likely want more reach, so if it were me, I'd get the 1.7.
Have you looked at what lenses you can get for the price of the TC? That could also be an option for you.
That's about $0.02 worth, don't you think?
WM