Well, long story short, my non OS version was defective, wouldn't focus anywhere near infinity, not bad for within 30 feet. SO took it back and ended up with the OS version.
So , I've got samples.
The first one is at 400 mm of a structure 1 km (more than half a mile) away. Myabe you can get sharper, but I'm not sure how. It was taken on the tripod with a 2 second delay to prevent mirror shake.
The next one is of a couple guys on skidoos maybe 300 meters away, probably a bit more, auto focus, in lens OS turned on hand held. I'm shooting through trees and stuff, I don't know how it could be any better at that distance.
The last one is also hand held, full reach (400mm) in lens OS enabled and hand focused. The lens kept focussing on the wire instead of the bird in auto focus. Nothing wrong with this one either.