We've published an update to VistaDB 5.0 to address a performance regression in 5.0.6 and a problem with queries against tables updated through explicit transactions that was introduced in 5.0. You can read about the latest updates and download the new release at:
VistaDB Latest Release
We've also published VistaDB 5.1 Beta 2 which includes these fixes as well as other items unique to the VistaDB 5.1 optimizer. This version of 5.1 is feature complete; we're just working on one new performance enhancement before we finalize 5.1 for release in April so we'd love any feedback, particularly if you've got a complicated query where 5.1 isn't outrunning 4.x or 5.0. Report anything you can to Support and then we can be sure it's addressed for 5.1!