To the OP:
I love my 8" JBL subwoofer and JBL is one of the better mass market audio manufacturers in business imho.
Crutchfield may not have rock bottom prices, but they do have excellent customer service and are actually authorized to sell everything they list, unlike a lot of other online retailers.
GC is the chassis code for the 1st generation Impreza coupe. AcquaCow Dave's speakers look like they're Pioneer Premier 720 PRS's, a beefy 6.75" component set that have been discontinued.
The 02-04 Imprezas are a pain to deal with in terms of front speaker depth. Idk what car speakers you we're looking at that were 7" deep. In order to get speakers approaching only 2.5" deep to fit without hitting anything you have to run 1-inch thick spacers in addition to spacing your door card off the inner door panel. I hesitate to recommend anything specific, without knowing more about your budget or the rest of your system, but a good starting place to look at imo are the Polk db/DXi and the Kicker Ks series.
I used to run Polk db6750 and Pioneer Premier D720 components in my 04 WRX. I have since ditched the extended door pins and extra set of half inch spacers and invested in a set of truly shallow (1-2/3" deep!) components. https://www.massiveaudio.com/product...nent-speakers/
In hindsight, I highly recommend doing the same and getting really slim speakers from the beginning. My original polks were 2-3/8" deep and still hit the window with a 1" spacer.
Also, the current iaperformance spacers are garbage. I bought them originally, expecting solid pieces like the ones in Dave's picture, but they're now just thin hollow plastic. Kartboy made solid plastic 1/2" spacers, of which I bought 2 sets but I believe they're discontinued now as well. Paranoid Fabrications looks like they make something similar and offer varying thicknesses. http://www.paranoidfabrications.com/...-spacers-pair/
Hope this helps. Good luck!