PowerColor's LCS HD 7970 has the highest base clock speeds out the door right now and this shows in the performance numbers. When overclocked, the performance margins increase in percentages close to the overclocking percentage increases. The highest stable clock speeds I have run on an air-cooled HD 7970 have been 1177MHz on the core and 1625MHz on the GDDR5 memory. On the LCS HD 7970, thanks to the ability of the EK waterblock to absorb the thermal load, I was able to reach 1235MHz on the core and 1730MHz on the memory, using a maximum voltage of 1300mv. These speeds are game-stable, not just benchmark-stable. Core speeds on the 28nm core of up to 1270MHz were possible, but the memory clock speeds had to be significantly reduced to accomplish this. Even then, 1270MHz was bench-stable only. It's always a game of compromises. The thermal performance and noise characteristics of the LCS HD 7970 were excellent. At stock speeds, the temperature delivered under load was just 42 ºC. When overclocked and under load, the maximum temperature was 44 ºC. PowerColor states that the card should not see temperatures above 50 ºC and my testing found this to be the case. This has to be put into perspective though. If your liquid loop cannot support the additional thermal load imposed by the addition of a video card to the loop, the temperatures will be higher than 50 ºC. My simple loop with a 3x120 radiator connected to the CPU and video card supported this additional load just fine and should be an ideal starting point for a CPU/GPU loop, unless going with dedicated liquid loops for the CPU and GPU. Using a water-cooled card means the noise signature from the reference or custom air-cooled is nonexistent. A 0db noise profile is just great and the EK FC7970-equipped LCS HD 7970 delivers silence to my ears. It's a welcome change from the loud fans I am accustomed to during testing.
Wow. 1730 on the mem. I was hoping the core would be stable at 1270 without sacrificing the memory speeds since the lightning can do 1265/1505, but I'll blame it on the lightning's higher quality components (ref. 7970: 5+1+1 phase, lightning: 14+2+1 phase). I'm sure that if someone can get their hands on a golden sample, 1300/1800 is possible on the LCS (maybe even higher on the lightning if someone does something like this to it).
I guess someone can use this review as reference for the performance capabilities of a watercooled 7970. Just an FYI for any potential buyers of this card: if it does retail for $800, you can buy a reference 7970 for ~$550, and the ek block for ~$125. You are basically paying the $125 price premium of having a single slot, pre-installed waterblock on your card. It's a nice read nonetheless
Edited by airisom2 - 3/19/12 at 11:25am