Originally Posted by tbzep

Add detail to the rocket such as hydrogen or atmospheric sampling scoops, deflector arrays, antennae dishes, bulbous fin tips/instrument pods, etc. and use thicker balsa fins to make the model more draggy. From there, add a bit of weight until it works out with the C6-5's. The actual detail bits can vary based on whether you want the model to look like a scientific research, civilian passenger, military, or other type vehicle.