The exhaust that was on the car seemed to be the original configuration, although the cat has obviously been replaced, and the muffler looked too good to have been original. All the pipes looked stock though.

The engine was actually MUCH louder than I had realized. I didn't know how loud it was till I stood behind it and revved it up. I knew that it had a high pitched crackle, but standing behind it, it was actually so loud that it hurt.

I bought a Magnaflow XL Performance polished stainless truck muffler that is 6" round and is 27" long (body length) with 2 1/2" inlet and outlet. These sell for about $109 through Summit, but I bought this one for $55
including shipping on E-Bay. I also bought a 2 1/4" polished stainless 90 degree bend for the outlet and a matching 180 bend to replace the stock 1 3/4" crimp bent pipe.

I was a little concerned that this muffler would be too loud, but it's actually MUCH quieter as far as tailpipe sound output. It does drone a little bit (mostly at low RPM and heavy loads, like when you start off from a stand still)
but overall I think it is as quiet or quieter than the stock system, without the piercing crackle. It now has a very pleasant "high performance  4 cylinder motorcycle" sound.

I've also installed a TRD header with mandrel bent 2 1/4" tubing from there to a new OBDII style converter. You can see the header in the lower pictures. Overall, the improved exhaust flow capability is REALLY helpful and
has a nice sporty sound.

My seat of the pants feel "quesstimate" would be 10 HP and 15 ft/lbs of torque increase. I know that seems like far too much of an improvement for this engine, but it really is THAT noticeable!
MR2 Exhaust