NFS@home I believe has super short run times. They are memory hogs but take only an hour or two if I remember correctly to test them on. I honestly believe hyperthreading in BOINC is going to depend on each individual project depending on whether or not the project is FP or integer intensive. It does not surprise me that you see the same with PSP run times because that is almost like Prime 95.
Cheers, I may give the dreaded NFS@home a test when I have some time - there will probably be some babysitting involved to get accurate results. Thinking about it, I've not seen any speed up on any BOINC projects when I've allowed them to wind down prior to non-BOINC work. Sorry for stating the bleedingly obvious re PSP