Yikes. The thermal paste was so old and crappy it came off in chunks. Didn't even leave a smear behind. I replaced it, and now it idles at around 101F; even a short gaming session only pushed it to 111. Quite an improvement! I still think I'll give the single-CPU approach a try, but it's nice to know that the normal temperature for the DP card is a lot more reasonable than 136F!