Today, I installed Boinc on a windows 7 pro system with I7 3770. First 80 work units average around 2 to 3 mins to complete. Then without changing anything the run times for the work units have increased to right at 3hours to run. I look at cpu usage and all 8 threads are going at 100% use and can't seem to figure out why.

Well, my i7-4790k will typically run a task at maybe 1,5h to 2h, so the longer run time mentioned seem very reasonable. Sometimes I and others get these superfast ones, but they are not the typical ones that you should expect. I didn't see one for weeks after joining. You were "lucky" from a credit point of view, however I have no idea whether these tasks have any scientific value.

Then there are small differences in speed depending on whether you are running standard, SSE or AVX tasks. The client will choose the fastest version after testing the supported alternatives. Your computer is choosing AVX now (normally the fastest but generates more heat), however one of the first tasks assigned was a SSE which is still reported as running.

I have several computers running (some AVX and many SSE) and I notice that these phenomena seems to be intermittent and also typically affect either the SSE or AVX tasks.

thanks I was just really scratching my head as to what was going on. I appreciate the feedback and will let them run. Just didn't know if I had some configuration issue or it was normal.