GN-1 3" dual on my current GN Legend.
I ran 3" Torque Technology (long since gone the way of the dodo) duals way back in the day on my 1st T-Type RUQWKNF.
I ran an ATR 3" single on my White Limited RARE T.
And a Pypes 2.5" dual system was on my Blue T Sarah when I bought the car. I never got around to upgrading it to 3" dual.
The others are correct. Sound plays a huge difference between all the different systems out there. I personally have always liked the dual 3" sound the best. And Mr.Spool is correct with his question. How fast do you want to go?
What I've seen is, once you reach that 550 flywheel hp range, it's best to consider larger diameter piping on these cars. IE going from 2.5" to 3".
Can a car make 700 flywheel hp with just 2.5" exhaust? Sure, but the engine might not be the happiest doing it.
Over the years, there have been numerous sound clip videos made on these cars. Most have been lost or deleted online.
I made one myself in 2018 after installing my 3" GN-1 exhaust system on Legend. You can check it out here.
In the end, it really boils down to what you like, especially if this is a pump gas, no alky stock engine bolt on street car.
Some single exhaust systems have drone while cruising, others don't. I know the 3" single shot ATR system that I had on my white Limited years ago, actually made me a tad queezy when I drove it from Central Mississippi to Bowling Green KY in "98, because the drone was so bad at highway speeds. Given, that was a 8 hour drive depending on traffic. YMMV.
Don't forget, the header system you choose to run will also greatly affect the sound and the performance/transient response/spool up too.
Hope some of this helps.
- Patrick