You may have recently seen articles that explain how Google will be checking the speed at which your pages load and will be using it in their page ranking system. I had read about it on the Register's article "Google tweaks search results with mystery site speedometer".
I then realised that a company I have worked with in the past has a tool that allows you to test this type of issue for your site and even allows you to record the results over time...
UbiKann tested on GTMetrix
Check out Gossamer Threads GTMetrix Site Performance Analyzer. They have just added a new system that allows you compare up to 4 reports/URLs. Oh and it's free, oh yeah... 🙂