thank you!
i use the uhd 1:1 preset and then just set the resolution to 3840*1536 in the submenu.
card spanning and overclock is required. i have a sandisk 170mb/s card that i overclock to 160mhz.
it's important to disable global draw, and your first recording of the session will only go for a few seconds and then stop. after that, long recordings are possible. if you don't clip too much, continuous is possible until you run out of space!