REL Stadium 3 vs. 2

I am considering adding another REL sub to my system. I currently have a Stadium 3, can anyone tell me what the difference between the Stadium 2 and 3 is?
Thank You,
Basically, the main difference is a power increase to the Stadium III. The II has a 100 watt amp, the II has a 200 watt amp. But since amplifier wattage is exponential, the stadium III is 10 TIMES more powerful than the Stadium II amp. The stadium III also had some minor changes to the ABC crossover. Thats about it.
Amplifier wattage is not exponential. Loudness is a logarithmic function of power. So a 200 watt amp will be able to play about 10 Log (2) = 3 dB louder than a 100 watt amp. An increase of 6 dB would sound twice as loud.