I had a slow task running on a GT240 (Vista x64 6.12 app, 4x GT240):
343-KASHIF_HIVPR_n1_unbound_so_ba2-1-100-RND9141

After 32h it was only at 90%
The alarm bells started ringing as this is a fast task type and should finish in about 15h on the 6.12 app.

When I checked the performance on EVGA Precision I saw some strange GPU behavour - the GPU usage was up and down so it looks like one task is running on one card, then another, and then back on the first, so in effect there are really only 3 cards running 4 tasks.

I looked in Windows Task Manager and saw an svchost process was using 27% CPU but only using about 48K RAM. I closed it and the graph went back to normal; 4 long straight GPU usage lines in EVGA Precision.