You can try read the
PPD Predictor thread, as it might give you a good estimate on WCG PPD you might expect.
These Q8x00 are Yorkfields, so you just have to multiply 5.5 by the speed of the processor to get estimated average wcg PPD.
Obviously, overclocked processors wiil get more points, but if you are keeping them at stock, i would estimate this:
Q8200 (2333MHz) about 12830 wcg PPD (1830 boinc ppd)
Q8300 (2500MHz) about 13750 wcg PPD (1964 boinc ppd)
Q8400 (2660MHz) about 14630 wcg PPD (2090 boinc ppd)