I noticed that testing after a PC restart with FF and IE using a direct link to the speed test I get higher speeds by as much as 1Mbps over the cap.
The test actually hangs for about 1sec and than it boosts up to about the middle. At the same time when it boosts the text at the top of the test page loads and starts to scroll.
The scrolling test might give inaccurate test results. I think it has something to do with caching the java script for the scrolling test. If it's cached the test doesn't boost anymore.

Also I never reached my full speed testing on this site but I reach it dling.
I think its because of my RWIN setting. Back when I had it higher the speed test would boost and give high inaccurate speed results and combined with a direct link to the dl test after a PC restart it would go over the cap my as much as 1.4Mbps.