Found the above tool it really offers some great insights into a pages performance.
It uses two sources for speed. Webpagetest which is a great tool with a cascade of timings for each page element, Yslow which is a browser plugin doing the same sort of thing.
Plus it evaluates the sizes of images and about 20 other factors which influence page loading and efficiency of code etc.
The speed of page load and performance is a factor in Google’s algorithm, if a sites metrics are poor it gets pushed down.