version 4 = first with the interior upgrade (digi clocks, dails, also better flow turbo that started with the v3.
version 5 = not much difference to the 4, slightly bigger i/c, different seats, minor changes.
version 6 = still the same old shape but considered one of the best from subaru in most places. again only small changes from the 4/5 but gave more torque.
version 7 = first of the new shapes, 6 gears, new package inside and out. most desirable would be the sti spec c! amazing car!!!! First car to start to overcome the lean forth cylinder problem.
This is of course sti's from japan. I don't know about american cars, but all cars here are from japan.
I'd still have an old 91 subaru legacy rs-r over most of the imprezas though. just need to drop in the sti gearbox. But then again, I'd have the old 95 evo3 over the new one so probably best to ignore me i reakon.