Make sure your BCLK clock speed is set to 100. Some auto tune utilities will set it higher and this could cause instability. Also an expected restart could also happen because of pcie bus, drivers or memory instability? Cubase can be quite heavy on cpu/memory resources so 4.3 could well be the limit for your system running Cubase. On the other had what’s the point in putting so much effort into getting it to work 0.2 GHZ higher. Mine is currently also on 4.3 and running fine.