I haven't heard v3 so I can't comment on it. However, from everything I've heard on these boards and the bit I've heard from Ian, has led me to believe there were major changes between the v3 and v4. I'm not just talking HP woofer and better tweeter. I think the mid was improved, definitely the crossovers and improved understanding of the family of curves.
I had all v2 including a 150 and 600 that left me emotionally distraught. The 80s couldn't give me soundstage depth and placement across the stage wasn't great. The QS8s were puny. The v4 was a God-send. I just can't say enough good things and I'll stop now because board members are sick of me crooning about it.
Keep v4 in mind as you create your roadmap.
