Well. When I was still REAL new to my road cycling but I was fit, on our 25km Tuesday ride at the end was a smooth seal road and we would come across the train tracks and turn left onto it, changing gears as we turned, and then go for it. I managed 54kmh one day. I got passed by some dudes doing 64kmh..... anyway. I have managed to hold 50+ on the waterfront riding solo for a few minutes with a slight tail wind (well maybe not THAT slight ) And another place you come down off a hill, cranking it up, and then hold your speed as long as you can on the smooth seal at the bottom. I managed to hold 58kmh for half a km, running my restricted gear of 52x17....man was I pedalling fast or what!

Regards,
Brendon