When I set the nexus to 200+ MB in the SED command line parameters, my game crashes pretty much every time I switch resolutions (1920x1080ish) with
Error E2005: Can't create DirectX texture unnamed.
With a nexus of 300 I get that error message before loading the first real level or the menu.
With a nexus of < 150MB it seems to be working for a while. Still got the error message with a similar or lower nexus after playing for 20+minutes on my laptop a couple of days ago, on a published build.

The RAM usage shows pretty much the same value (~1055MB), both for a nexus of 150MB and 250MB. Does that make sense?