Update on rear diffuser with STI axleback:
Everything fits great, no rattle or rubbing. The midpipe comes closest to touching the rear diffuser but the muffler itself has plenty of clearance.
My MPG has gone up by 2.6 MPG, according to my Fuelly app with no change in how I drive.
The diffuser looks great with the STI exhaust and is high quality stuff. It really completes the rear end. I love how it looks from the back now.
