Between RSX and PR5. first of all, I like both of them.
My RSX is the base type 5-speed manual, it has 160HP and 141lb-ft of torque. At low rpm accelartion is just ok until it gets above 3000 you can feel it really kicks. The auto transmission PR5's acceleration is not very impressive, I am not sure about 5-speed manual but I think it should be better the auto. Since the car is still breaking in I'd better take easy on that.
PR5 has better ride quality than RSX, not very firm but not harsh or punishing.
I think Mazda did pretty bad interior design on PR5, there is no cup holder or ashtray for back seat!!! That is unbelievable RSX has 5 cup holders even though it only can sit for 4 people. Both of them have leather seats, PR5's seats are bit softer than RSX's.
For carge room PR5 definitely gets big plus over RSX.
That is all I can think of right now, I will put down more later on.