The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
Just to follow up here, thanks for the suggestions and help. I kept having crashes until i changed my G-sync settings in the Nvidia control panel to "fullscreen and windowed" mode. The SLI on or off didn't make a difference. Once the G-sync setting was changed I've played 10-12 hrs with no crashes where before it was 1 hr max.