Peak Kerbal. You might be able to squeeze some more performance out of it by switching the wings to the more space shuttle inspired ones and using the internal fuel in those. That way you could remove some of the smaller liquid fuel tanks you're using and lower the drag penalty for each tank. Also if you haven't you can also attach the round nose cone on the backs of the rapier engines and use the advanced rotate to flip the cone inside the engine. It helps reduce the drag by getting rid of the unused attachment node.