A lot of people are in similar boats. In fact, if EE had updated their forum a year or so ago, they might have hit a gold mine since people are leaving VBB in droves! The short and sweet basics are:
1. VBB was bought by a public company and did things which angered a lot of their base.
2. The newest version - 4x - is not liked by a lot of older VBB users! They feel that 3.x is the mature app (shades of EE here?)
3. The VBB public company was then bought by ANOTHER holding company…my outside assumption is that they failed in many ways (Internet Brands), and were forced to get out.
4. The lead developers at VBB responsible for up to 3.x left the company and started Xenforo - they are being sued by their old employer (the holding company, now).
EE is vastly more integrated with the CMS parts - and much better for creating a complete site with - than VBB and most other forums.
But EE has been hot and cold on upgrading and caring for the discussion module, and it remains to be seen if they have the resources, desire and programming power to catch up to the newest features.
Super, I don’t think there are any EE forums with that number of posts - and without such, you have no idea of whether it could even do the job! We hit a wall last year, but the wall came down when we upgraded our dedicated server. Still, VBB is known as handling larger sites than EE (just due to the number of sites, you have more examples!)......
So, what to so? If I were you I would not move to EE until I saw a couple sites in EE with that number of posts…and, just as important, the max number of online users at one time…so you can gauge whether it can scale up.
I don’t think the VBee thing is right for very large forums - it is great for those who have EE and then want to use VBB as the forum module, etc…..
Short and sweet, my suggestion would be to stay where you are for now and look at what XF does over the next year as well as EE. If you need lots of crazy add-ons, you probably won’t want to move to EE…..not as many people developing (an understatement!) for the forum….....
On the other hand, if EE changes course and decides to be a forum “player”, I can attest that their forum is stable, works well and was able to do the vast majority of what I needed it to do….I’ve been using it since 2003!
I also use the other parts of EE to some extent…...I will likely still use EE even if I switch forums sometime in the (far) future!