Your better off running 2 sticks, cuz with 3 your not utilizing the dual channel technology. It increases system performance.
Unless you have 2 sets of sticks.
From the cpu-z screen, where it shows Dram Freq 100.5.
This should show 200, your underclocking your ram if Im not mistaken.
Also on the other screens, that show the ram timing for each ram slot, this screen just shows your the manufacturers timings & frequency.
If you want 200 mhz which is DDR 400 you would run the ram at 3,3,3,8.
You also mentioned that when there are dimms in both the 2nd and 3rd slots the pc
registers DDR200, but if its any other combo (1 and 3, 1 and 2) it registers DDR400.
Thats how dual channel & single channel work.
If you want dual channel, you have to install two identical ram in the colored slots.
If you look at your manual it will show which ones need to be installed in which slot for dual channel.
Please make sure you know how to reset cmos incase you choose a setting which doesnt boot.