Makes no difference at all. The guy that's going to win the sprint is going to win the sprint if he has a 5 lb disadvantage.

In the first place you're starting your sprint from 28 mph or more so that the majority of the energy required to drive the bike is from wind resistance. Secondly, a lb or two difference just doesn't make enough difference when you count the 140 lbs of rider.

In engineering we generally allow as how a human can tell the difference in something like 2% of anything requiring strength. If your bike weighs 15 lbs and you weigh 140 the combined weight is 155 lbs. That means you should be able to discern about 3 lbs of weight difference if you're a really sensitive person.

I could tell the difference of 10 lbs of lights and wet cell batteries on my winter lights on my mountain bike but that was only on really steep climbs. I weighed 190 lbs and my bike in those days without the lights weighed 36.

So on steep climbs I could tell a 4% difference. But it was pretty plain since I had to go up the 40% climbs a gear lower than usual.