I modded my Skyrimprefs.ini file with additional commands for better performance (e.g. bUseThreaded..., loadinbackground, etc). I also upped the shadow, texture, water reflection resolutions. Even though my frame rate was high at bout 50 frames per second, it was giving me random CTDs combined with hi res texture mods. I didn't realize the tweaked Skyrimprefs.ini was the problem until I deleted it and started over with a default one. Before I was sometimes getting a CTD at around 10 mins, then later on it became a reliable CTD at about 8 mins. Now I get no CTDs, or at least none after a couple hours of running the game. Maybe a tweaked Skyrimprefs.ini or Skyrim.ini is not working well together with some of your textures.