I had that, then got another charger road and track package without the STP - But there seems to be some confusion about it still.
STP adds, like another member stated, bigger front and rear sways, it DOES NOT add the 3.06 axle - the road and track package/trim level adds that automatically; even though Dodge's description of the STP says '3.06,' the 3.06 gears are already present on the Road and Track trim level. All other chargers get the 2.65 gears, and it makes a big difference in acceleration times. The Mopar 2011 has 3.93 gears, and I believe the 3.93 gears are also on the 2012 SRT8.
The STP adds better brake pads, and an 'improved' brake feel - but that is it - the calipers are the same, and the rotors are the same.
The STP deletes the Nivomat shocks and struts, and adds monotube shocks (Monroe, I think) that are stiffer and gets different struts as well.
STP also adds the Goodyear F-1 Supercar summer (3 season) tires.
Most importantly, the STP adds a different steering rack, with faster ratio steering.
I was confused about the specifics, so I wrote an email to Dodge and asked them, and that was the response.
The STP makes a big difference in handling, IMO (having owned 2011 versions of the car with and without the STP), but the ride was too stiff for me. I much prefer the 'regular' road and track suspension for daily life, but I miss the great handling of the STP - it turned this car into a big fat Mazda Miata. I di wish Dodge had at least given the 'regular' road and track package the better sways and steering.
Even though the road and track suspension is tuned to be stiffer and more sporting than the 'normal' chargers, I wish it handled as well as the STP but with a little softer damping. Guess you can't have your cake and eat it too with Dodge - My G8 GT had a suspension that handled as well as the STP, but was far more forgiving with potholes and bad roads.