So let me share my experience. I have full STEP 2.2.3+ extreme max everything. After finishing that install, I started crashing all the effin time to the point where I gave up for a bit. I then posted this thread and took Flytraps advice.  As you can see in my screenshots in that thread, every time my RAM hit 3.1+, insta crash.  I downloaded Optimizer Textures as per Flytraps advice and the ONLY option I checked was to resize if size was > 2k, and ran it on my whole Mod Organizer mod folder.  After it was done I have yet to crash, and the visual trade off was almost unnoticeable for me, it still looks great.  Here are my last two skyrim runs after texture resize, each is several hours of play with no crashes.    As you can see I never hit 3.1 GB RAM, and even though my VRAM is maxed out the whole time... no crash.  I think STEP is gonna have to start recommending only 2k textures after a certain point because everyone is gonna start crashing like this, and as others have said, its a Skyrim being 32 bit limitation, not a PC hardware limitation (I have 16 GB RAM, SSD, 8 core CPU, the works)