I've got a supercharged IS200 and an MR2 Turbo.
You can't really compare the two, they are just too different.
The IS200 is a great car in supercharged tune, it has bags of torque, and a great whine when you fit the induction kit. Lovely car to drive, comfortable, all the toys etc.
MR2 is more for 'outright thrills', good fun to drive, fast etc
Like I say, you can't compare the two.
If your after power, steer away from a standard n/a IS200, they just don't cut the mustard. Go for a supercharged version, or get the Altezza with the beams engine.