Jeff, the v4 tweeter has a metal screen as opposed to the plastic lens on the older version. You wouldn't have a v4 tweeter on a v3 speaker unless you got one from Axiom and replaced it yourself.
Even if you have a v4 tweeter, you likely don't have a v4 crossover in your v3. This makes such a big difference in everything!
Please trust me when I tell you that M3v4 is so vastly superior to previous versions. I hated the M3Ti and now I will never let my M3v4 go! I can listen to it for hours with all kinds of music.
v4 is truly a gift to mankind.