I just picked up and installed the GReddy Revolution RS catback exhaust for the IS300 last week.
This is the only 3in catback available currently (to my knowledge).


Here is a link to it on GReddy's website:

http://www.greddy.com/products/exhausts/revolution-rs/


A neat plus of this exhaust is that the tips are removable, and they offer different materials and styles. Since have a Sportcross, I plan on buying the middle titanium tip thats a few cm longer than the small SS tip that came with the exhaust (to clear the bumper better)










This pretty much shows how much difference in size the piping is. The GReddy is ~76mm, the JIC Magic Bullet axleback is 60mm, and the oem B-pipe is 52-54mm (that's REALLY narrow for a 3.0L motor!)


This is the exhaust installed minus the tip. I took it off for test fitting on the Sportcross. Due to the different shape of the wagon's bumper, I needed to dremel the opening a tad larger to fit the tip in a way it didn't touch the bumper at all.
As you can see, my old exhaust had already melted part of the rear bumper at the opening due to it being angled.



Overall, I love it.
I can't say if it added any hp/tq over my old setup. The car definitely has a meaner growl to it than it did before. At cold idle, and on acceleration. At cruising, it's almost the same as before, just with more bass tones.
If you want to see videos, there's a bunch on YouTube. I watched a bunch of them before I bit the bullet and ordered this exhaust.

 

I have the same one on my car and I like it a lot too. I need to get my downpipe modified though because mine doesn't fit quite as good as yours. My downpipe is meant for a top mount manifold and I'm using a cast treadstone. I'm honestly not even sure how it fits right now being that the dpipe is probably a few inches too tall.

Anyway, nice write up. I can definitely vouch for the build quality of this exhaust part. Worth the money, and fits perfectly in a stock exhaust system.

 

I should probably mention, currently I am a lightly modded non-turbo. This exhaust is bolted to the stock 6-2-1 OEM exhaust manifold and Y-pipe. I do have some slight exhaust leaks at that location, but nothing large enough to generate any noticeable noise (or heat) that I can hear in the cabin. I believe this is due to the rather large flange differences at this point. It's 52mm piping (2.25 flange?) on the header side and 76mm (3in flange) on the GReddy side. It also doesn't help that I put a used (previously crushed) copper SCE 3in gasket here, because I plan on swapping out the whole header for the FIGS within the next couple weeks.
If someone was going to bolt this exhaust up to any aftermarket Y-pipe, the flanges should seal even better than mine.