I also use a 43" 4k monitor, and I have no problems. I have display scaling set to 125%.
3DXchange does not crash for me, although there has been other reports mentioning that.
I changed the DPI scaling setting, because the UI font is indeed small:
1. Have a shortcut, right-click and select "Properties".
2. Click the Compatibility tab and select "Change high DPI settings".
3. Check "Override high DPI scaling behavior" and select "System (Enhanced)" from the drop-down.
4. Click OK and OK to close the dialog.