I used VB for just over 5 years. The last 12 months of that was VB4.x. In that total time, my forum had gotten a total of 180,000 posts. (the stats I got was from the wayback machines earliest stats, being Feb this year, 187,000, so about 180,000 two and bit months prior in December when I converted over).
12 months after converting to XF, my postings have now just surpassed 300,000.
I'm no mathematician, but I have noticed the difference in user interaction with the site significantly changing from VB to XF software, and the stats don't lie. That's around 120,000 posts in one year using XF, compared to 180,000 posts in just over 5 years using VB software.
Toss into that equation, my search traffic took a huge hit and recovery for six+ months changing software, nevertheless, user interaction still skyrocketed for repeat visitors.
The figures are now heading towards 15,000 monthly posts... I've never seen user interaction like this in over 6 years with my main site, until XF software.
So whilst one could compare XF to VB3.x for performance, which they are close from what I have measured. This is where things break apart from decade old software to current trends in software design. VB3.x never enticed users to post like XF software does.
When I changed, I anticipated 250,000 posts by the end of this year with XF software, factoring in the like-ability of the ajax inline posting, editing, alert features, streams, etc... well and truly surpassed my expectations, as my search engine traffic has only recently surpassed my traffic when at the end December 2010, converting from VB4.x to XF.
My return visitors and user interaction is what's showing the significant growth, and the numbers don't lie. Search traffic has pretty much tapered back out and slowly growing on the posting ratio (new content > search referrals).
So I now have an adequate comparison to VB3.x software, none of which ever showed such user excitement to interact with the site and other members via its software, compared to XF.