gnilaeh,
The info in CPUz is not correct but represents the max speed your SPD is reporting - based upon the settings in your BIOS. Get the BIOS to recognize the 1066 and CPUz will report it as such.
The first thing you need to change in your BIOS is the voltage for the DRAM. Your native voltage is 1.8V - raise that to 2.0V or 2.1V. This alone may make your memory come up as 1066.
Once you've done that and tried it, go back into the BIOS and set either the RAM speed directly, or the multiplier for RAM speed. Turn off the "auto" setting for the RAM and manually set it. Settings that weren't showing previously at 1.8V may now be available to you.
Once you get this memory working, you may want to try using all 4 modules. If you do so, it will all be set as 800. That's not bad, since the speed you gain from the extra RAM will more than make up the the slower speed. And many would argue that the RAM running at 800 with lower timings is faster anyway.
Will both pairs work together? Have to test and see. Make sure the pairs are in their own color slots. Both new ones in one color, both old in the other color slots.