One of the iterations of my exhaust was the LC Engineering header and cat-back. Was nice on the highway and higher RPM, but it didn't do much in the streetable RPM range.
The way it is now:
Stock manifold and downpipe until it merges into one pipe.
That connects to the Cat which is 2" diameter inlet.
Then it's 2" dia until the muffler which is 2.25" dia.
Then it's 2.25" out the back.
Seems to keep the engine happy in the 1500 - 4000 rpm range, about where I keep it for driving.

Todd

1986 Pickup extracab longbed "Woody edition"
SAS - 33's, 5.29's, lockright rear.

02 IS300 SportCross - my "DD"
94 2wd v6 extracab
04 Outback Wagon- wife's/family car