Resources to learn about the pipeline/memory?

When benchmarking my OpenGL code, I often run into behavior I have trouble explaining. Like higher FPS when drawing more vertexes, or even when just doing more CPU stuff. I assume I'm running into the details of how the pipeline works, how memory is being cached, and how my driver works. I have no idea how my code would work on other hardware.

I would like to know more of such details, but the webs seem to be full of misleading tutorials and uninformed opinions (at least when it comes to modern hardware).

So my question is; Where do I go to get a handle on this stuff? The best I've found so far is the "An intro to modern OpenGL" posts at duriansoftware.com. Are there any websites that aren't clogged with people trying to get a quad to render?