Here is something for you first, I already gave this link before, but now I found something interesting about it. The source is the same as your link on the virtual particles.
Follow your own link: http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html
and then click the link at the top of the page saying Physics FAQ.
In this Physics FAQ you will see the link to the article about the virtual particles again. You will also see a link to an article with the name:
Is the speed of light constant?
If you read this article you will find out why the values of c were measured higher in the past. You will see in the conclusion that the speed of light has not changed.
Interesting isn't it? There are actually good explanations why the values for c were higher in the past and it has nothing to do with a higher speed!!