Changing the virtual mem back didn't help. Kept crashing at this resolution and even 4k. Started to optimize scene more and hide stuff not in view (does that actually do anything?). Same result. Bumped displacement screen size to 6 and now it renders fine with like 20gb less ram used for that scene. Wonder how big an effect the new 2.5D displacement actually has. Will try and render without it later if time allows.