The stats have been posted in this thread and others before it from a source that didn't take certain things into account.

Basically the more armor you encounter (armor on armor that is) the higher your default rocket will be compared to the Pilum because it has an explosive component to it. The Pilum has a higher average damage, but since its purely impact damage you'll do less damage with armor reduction unless you're hitting the soft spots of armor. This difference varies depending on what you hit, where, when, and how you hit it.

Several other factors come into consideration that people have not tested or haven't cared about. The pilum, as a fired round, probably has a range maximum/minimum that will affect its damage. However people rarely care about that because unless you're as sharp as the guy in the video I posted you aren't going to be hitting jack at medium/long range moving targets.

The EU default rockets are also a cluster of rockets which can affect your damage if you're making a glancing or inpercise shot. Basically while it's grouped closely together it is still a 'group' and some rockets may miss or hit a spot of higher armor on the target. This will vary the EU damage against precision targets (like the underside of an APC) greatly because of the difficulty of stringing several rockets through one very small hole.

To counteract this the EU cluster has a higher average damage than the PAC single shot, and both do more damage against high armor than the Pilum because they have a longer reload and have to maintain LoS to guide them in.