This isn't solid information, but on a whim, I did a clean uninstall/reinstall of Crysis. By clean uninstall, I mean I deleted the folder in MyDocs, and the entire Crysis folder in the Steam directory before I reinstalled. Before I installed MWLL, I launched Crysis to create my profile. Since then, I've been getting 50+ FPS on DX10 Very High (32-bit)...even on Thunder Rift! Now, I haven't been in any match larger than 15 players or so, and that might be the key factor. I still freeze up for 5 seconds or so at random, but I've had that issue since 0.1.0.
Edit: Just got out of a full 12 on 12 match, and framerates were just as steady. Also, I'm not using any of the CCC packs, pure vanilla Crysis.