Brian: the speed limit is not some magical number that is safest to drive at. Driving slower than the speed of traffic is more dangerous than speeding up 5 or 10 mph. That doesn't make it legal, it just makes it safer - for you and everyone else. If you're willing to put yourself at risk to maintain the speed limit, that's your choice.

EDIT: And deliberately speeding up and slowing down quickly in front of a tailgater is the most unsafe of all.