Some quick results based on GeForce 7900GTX (650/800), with stock cooler at max speed. Note that test results were obtained immediately upon applying after market thermal pastes. I will update these results after 7 days as per recommended by Arctic Silver & Zalman. Tests were conducted on an open test bench with room temperature recorded at 28ºC throughout the test. GPU was loaded using ATITool's "Show 3D View".

Stock TIM
GPU Core Idle: 45ºC
GPU Core Load: 62ºC

Arctic Silver 5
GPU Core Idle: 45ºC
GPU Core Load: 63ºC

Zalman STG1
GPU Core Idle: 45ºC
GPU Core Load: 67ºC

As you can see, the STG1 did not impress me that much... at least during the first day of testing. Right after application, the AS5 is easily better than STG1. When compared to the already hardened stock TIM, AS5 was just 1ºC behind it, whereas the STG1 was 5ºC behind.

During my testing, I found that the STG1 to be quite watery when compared to AS5, Ceramique, stock TIM or any other TIM I've tested. So, I hope to see better results once the TIM has settled in. For the record, I double checked and reapplied the STG1 on the GPU core just to make sure that the TIM spreads evenly.

Thanks to Moderno for providing the sample. Look forward for a comprehensive review on my website soon.