Dual vs Single CPU question

1.25. Higher clock will do better for mentioned purposes. You can quite easily overclock it to 1.67 GHz (a little soldering required).

 

1,67GHz stable in a MDD??? I heard the max stable was 1,5GHz, that's interesting. I mean 1,5GHz was even the highest that third party upgrade suppliers would sell (for the 7455) http://lowendmac.com/ppc/power-mac-g4-upgrade-guide.html

Do you add additional cooling?

 

If you are going to do most of your stuff in OS 9, and AREN'T going to use a multi-processor-aware app like Photoshop, then the single 1.25 GHz will be faster.

If you're mostly going to use OS X, then the dual 867 MHz will be faster.

Other note: This is assuming ALL other aspects are equal. In reality, the 1.25 GHz model will likely have a much faster video card, more+faster RAM, and a faster hard drive.

In all likelihood (barring one of the two being a different model with an upgrade CPU,) the two you're talking about are the:
1.25 GHz MDD and the
867 MHz DP MDD.

Although given the choice between those two, my OS argument still stands.