I opted not to answer this thread because I assumed you would rather hear accounts from other customers rather than an employee.
Based on the feedback we've been given, DBSEO is marginally faster than vBSEO. Our own tests on this forum, however, showed a 33% decrease in page load times after we replaced vBSEO with DBSEO.
It's very much a "your mileage may vary", but I can guarantee you that DBSEO will not be slower. There is currently one feature that we are in the midst of investigating the performance impact of for large sites, but thus far that is the only report we've had of any form of slow-down.