I like your point no. 7 as it is what I thought as well.
It was very visible in Crysis when looking into one direction after fraction of second FPS would rise, but sudden change of scenery (eg. looking away from sea towards build up area or forest) would initially drop FPS by quite some margin (only for fraction of second again but more than few frames).
This also suggest that by increasing CPU speed we can expect these spikes to get smaller and eventually disappear.
I wonder about another possibility when CPU is so much ahead of GPU that it idles in between frames and goes into C states, can this affect frame rendering enough to matter? I know Intel's Speed Steep is fairly quick in changing between states but with aggressive power saving profile it still adds latency to every task. AMD K8-K10 implementation was pretty horrid and for gaming it was always best to disable C'n'Q all together.