2.5in exhaust will yield better low end torque, awhile the 3 would help high RPM breathing and HP. Bigger pipes will be a bit louder. Flows are stupid loud in the cab, so be prepared to hear it, all the time, no matter what, drumming at your ears. Besides that, only reason I don't like flows is because everyone has them. Ultimately, its up to you.
250 for a full system sounds purty good to me
