Well. To begin with, there is no v6 on the Studios (yet).
I own a good number of .v3 (40s, 60s, and one of the centers). Moving to the v4 changed the aluminum tweeter to G-PAL, added some bracing, and replaced the mid cone material. In my experience it's an improvement, but not dramatic (at least not on the smaller units, it would be interesting to compare one 100 to another).
The v5 is a more signifigant change visually. Unfortunately I've not had the chance to do an apples-to-apples comparison (perhaps I shouldn't post "I don't know"

), but perhaps I can manage one this weekend.
The short: Paradigm lovers do love the v2-v3s. Non-Paradigm-Lovers don't love any. Though there are improvements: between v3 and v4 at least, they are not "night and day".