Woot!!!
You're using two PSU'S!!!

Why?
That 500Watts PSU not enough ka?

Nice results there but having 8ºC drop in GPU temp by just changing thermal paste sounds ridiculous. Don't get me wrong but you could be mislead by your setup.

Firstly, I see that you are using dual 7300GT in SLI mode. So, there should be two GPU core temperatures displayed in NVIDIA Control Panel. Since you are only showing a single GPU temperature, I'm not sure if its GPU1 or GPU2.

Secondly, I see that you have a Delta fan blowing towards the GPUs. Not sure if the fan was there during the initial test w/o the STG1. If the Delta fan was there from the begining, it should be in the exact same position. If the fan moved a little, the fan could be blowing towards another direction from where it was originally seated.

Thirdly, you didn't provide any ambient/room temperatures for your setup. Room temp could have dropped after the initial testing w/o the STG1. You also didn't state the stres (100% load) or idle duration for both CPU/GPU. You have to make sure the testing period is consistent.

Lastly, I noticed that your GPU temp (with STG1) did not increase when overclocking. At 500MHz, its loaded at 49C, and maintained 49C even when overclocked to 620MHz. I suspect the GPU could have reverted back to stock clock instead of staying overclocked. This is why you should have RivaTuner's Hardware Monitoring tool running throughout the test.

I hope you don't get me wrong here but we appreciate your effort in doing these tests. Its just these few little things that you need to consider before doing such tests. On the other hand, your CPU results seems to be pretty consistent. 
And btw, the original thermal paste on the 7300GT is not by NVIDIA... its applied by Galaxy. NVIDIA doesn't sell 7300GT with Zalman coolers.

Actually you no need to be pro lah.
I'm sure even normal user will feel weird when they see the GPU temp at 500MHz = 49C and overclocked to 620MHz also = 49C. Besides, having 8C drop by just changing thermal paste is a miracle, unless the original thermal paste was insufficient.

bulibulizaimon, can you please check again to see if the GPU temp is still maintained at 49C even when overclocked 620MHz? This time, have RivaTuner Hardware Monitoring tool runing okay.   

I'm seeing a few users here experiencing higher temperature after applying STG1 (before cure in), which seems to be similar to my experience. For some reasons, you happen to be the only one to obtain better results after applying STG1.