123W Peltier help needed

I ahave a question and want to know if Im making a logical error here.
I have a 123W Peltier which runs at 15V max.
Im using an Enermax 420W ATX with 16A at the 12V output. I plugged everything together with my watercooling rig but without the cpu, to make a testrun and see how cold it gets. Clamping pressure was as much as I could press with my hands and arctic silver was used between block, pletier and coldplate. When switching it on, the best I got was 4degrees celsius at 23degrees roomtemp. Thats only a measly 19degrees delta. The Water didnt even get warm yet, so its not that I couldnt pump the heat away quickly enough.
So my conclusion is: I need more volts, 15V and not 12V with approx. 9 Amps.
Does my conclusion make any sense or am I mistaken somewhere?
btw you can see my rig with tons of pics here.
Thx for any help on this.

your peltier would absolutly love to be at about 20volts and 15amps for the sweet spot, dedicated psu needed. I have the 450W enermax and still had to go seperate psu. Also, you need to consider dissipation, that peltier plus your cpu wattage equals about 200 watts, a single radiator with 120mm fan dissipates 100 watts, a double does about 190 watts, a cube AND single will do around 250watts- without dissipation, you will just be insulating your cpu, not cooling it.

The Peltier is only rated for 15V, should I go over that? Wouldnt that damage it?
About the heat dissipation - I agree the radiator isnt efficient enough, Ill have to find a bigger one.