Need a little more data to be able to give an opinion.
CPU speed original and overclock.
Vcore
System temp and ambient (if you drawing outside air through your radiator)
and are those temps idle and full load or just average use? (If the ~42C temp is full use for an overclocked AMD then your getting real decent temps for a watercooler).
And amount of water only changes the delta of the temp (how long it takes to get warm and get cool), not how well it cools.
Also explain where your radiator is and what air it is using.
..................edit....................
I also found a shim to really help when I mounted my waterblock to keep the block flat on the core with the spring loaded lexan holddown I was using. I used pretty high tension though. You can make a shim with silicone though. Get a really nice level surface and put a small amount of oil on it. Then place 4 small buttons of silicone on the edges of your chip and place it facing down on the oiled flat surface and press down evenly in the center being careful not to rock it and then let it set. It should come off the oiled surface easily and then you can trim the tabs up to look nice if you want. And you now have a free shim.(non-conductive too...........

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