Roger is right, but here is a simplified view assuming a skilled sailor (75-80 kg) on a 105 liter board in 20-25 knots on flat water.
Power - 6.5 (it's bigger than the 5.5)
Faster - 6.5 (if you can maintain control)
Control - 5.5 (it's smaller and has cams)
If both sails were the same size then it's different
Power - about equal
Faster - cambered
Control - cambered
With that said, I have non-cam sails from 4.0 - 6.0 and cammed race sails from 6.6 - 11.0.
For me, the non cam sails on a bump and jump board are more fun than the larger sails on slalom, and formula boards.
Speed wise (I always carry a GPS), my 5.2 on my bump and jump board has the same top speed as my 6.6 on my slalom board (different wind conditions).
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.