If the segment is flat or slightly downhill and someone is on a time trial bike or even just has clip-on aerobars you can expect they are gaining about a mph from that equipment, at least. Also consider that top time trialists can average over 25mph for 100+ miles. Or 35mph for short events (I think LeMond was one of the first to break that barrier and he did it with aerobars).

So yes, engine, engine, engine but don't forget about equipment and rider position.