Below you will find various RPG statistical data that you will find useful in the Bad Company 2 PC Beta.  Unless DICE changes RPG Damage, or Weapon Armor, on the retail version, this is what you can expect.  Credit goes to Stinger911 on the Steam Forums for posting this information:

Carl Gustav vs Bradley
Front: 5 hits
Side: 3 hits
Rear: 3 hits

RPG vs Bradley
Front: 4 hits
Side: 2 hits
Rear: 2 hits

Carl Gustav vs Anti-Air
Front: 5 hits
Side: 4 hits
Rear: 3 hits

RPG vs Anti-Air
Front: 4 hits
Side: 2 hits
Rear: 2 Hits

Carl Gustav vs Bangbus
Front: 1 hit
Side: 1 hit
Rear: 1 hit

RPG vs Bangbus
Front:1 hit
Side: 1 hit
Rear: 1 hit

Carl Gustav vs Main Battle Tank
Front: 5 hits
Side: 3 hits
Rear: 3 hits

RPG vs Main Battle Tank
Front: 4 hits
Side: 2 hits
Rear: 2 Hits

Conclustion: Long story short?  The RPG does more damage than the Gustav no matter what vehicle you are shooting, which was expected.  The launchers do the least amount of damage to a vehicle’s frontal armor in all cases, though with very lightly armored vehicles such as the bangbus and ATV, this of course doesn’t matter.  Rear shots do SLIGHTLY more damage than side shots, but not a noticeable amount. In almost all cases, it takes the same amount of rear shots as side shots to destroy a vehicle.  As a side note, I DID somehow destroy the Bradley with one rear shot from the Gustav, leading me to believe that there are weak points on the vehicles (similar to the frontal tank treads in BF2) but I have not identified them yet.  This testing also does not take into account the armor specialization upgrade you can use to make your vehicles more durable. Not sure how much more protection that adds.