GeoSuite2008 on "[Plugin: W3 Total Cache] First Byte time very slow"

I have the same TTFB problem. In fact, I have 2 problems.
1. I have W3 Total Cache installed. However, the http://www.webpagetest.org/ test shows all cache static failed.
And the TTFB is between over 8s to 2.747s (resun)
My site is http://geoadvanced.com/

2. It seems that W3 Total Cache increases TTFB. I use a test site (http://geoadvanced.org/) to test the TTFB. Below are the results:
No Cache WP Super cache W3 Total Cache
1st time 0.385/0.516 0.380/0.294 0.887/0.717
rerun 0.738/0.262 0.313/0.265 0.672/0.676
1st time 0.532/0.262 0.272/0.266 0.778/0.687

Any suggestions and solutions?
Thank you.