Every time I see this problem (Purple or Black textures) it has turned out to be a memory problem, and the mod user just cramming their machine with resources their machine cannot handle, DLC + every mod I fancy = Machine go pop. The DLC textures being a common factor.
Anyway, to be sure, here's a very useful tool - http://skyrim.nexusmods.com/mods/6491, it has one problem trying to display FPS in game for those with ATI Graphics, the rest of it works fine for them though. For NVidia users its brilliant.
It will give you loads of stats of your game session, including RAM and VRAM usage. So you will see if you are topping up your machines memory limits with excessive amounts of Textures, meshes, sounds etc. I am running the current beta, testing my mod with other mods textures in game on High game Texture setting, and doing that comfortably with only 256 meg of VRAM in my laptop (minimum spec for the game is 512), always having circa 40-90 meg of VRAM to spare, with an occasional load spike taking me up to just under 250mb used

If the graph for you with either RAM use or VRAM use is flat-lining at your upper memory limit for either, that will be a good area to try and reduce and find out what is filling your machine up and causing bottlenecks in data transfer between parts of your computer.