Extra speed on a "better" bike can come in different ways but they mostly originate with the rider. Eg: you feel more confident at speed and therefore take hills & corners quicker. Or, the frame absorbs more bumps and you are able to ride more relaxed - which consumes less energy over a longer race and thus you are fresher to ride quicker. Extra speed rarely comes from riding the same piece of road in the same way as you would on your "slower" bike. Hate to say it but.......its not about the bike.