I recently put the OEM exhaust back on and there's definitely improvement in the lower rpm torque but top end seems somewhat restricted compared to the taitec center exit I had. I would suggest going with quieter aftermarket exhaust so you won't suffer the higher RPM range.
I actually would prefer the trade off of better low end power and loss of little top end. I'm a very slow driver(far right lane) anyways so it wouldn't bother me that much.
If you don't mind me asking, what prompted you to switch back to OEM? Do you have headers?