The newest version of prime should do the trick. For ORthos run two instances and open task manager then go to the processes. Right click on one of the orthos and click affinity. Set one to cores 0 and 1. Set the other Orthos to cores 2 and 3. I prefer Orthos even though it is a bit more work. I also have taken a liking to OCCT due to its ability to log data.
... as this newest version will auto-detect and stress all four cores of your Q6600, without the need of running four separate instances of Prime. The x64 version filename is p64v256.zip, and the x86 filename is p95v256.zip