Massive exhaust leak and low-end torque

An exhaust flange rusted out on me, so I had basically an open pipe ending behind the rear cat yesterday. Maybe it was just trepidation at pressing the LOUD pedal, but it seemed that the car produced very little power below 2250RPM, versus its usual production of adequate power from 1750 on up. Unfortuantely, my experience is no scientific study of exhaust backpressure (I'd love to dyno test an exhaust with a variable restrictor plate). An anecdote is all I offer.

That, and advice: If an exhaust flange rusts out, replace it with a split flange, such as they have at AutoZone. Installation is very easy. I'd rather have stainless hardware, but AZ was the only place open on Mermorial Day.