And, my favorite part, the Flex's.
There's always conflicting info about what parts are compatible between Imprezas and Legacies. Subarus are like Legos - remember that statement. If individual parts don't fit, the whole unit usually will. Yes, top hats and spring diameters have changed. Yes, the orientation of the tophats in front is different between the BD/BG/BF/BC/BF/BE/BH/BP/BL?GC/GM/GF and the '02-up Imprezas, but that's relatively easy. You've got two options. Get a suspension setup designed for one of the former cars, get a set of tophats for your specific supesnsion setup that fit one of the former cars (and has the right spring diameter, if you're using a standard spring), or get an '02+ setup, and swap the front hats side to side. Now, the only time this matters is if you have camber plates.
Here's why: the only difference is about 30 degrees in orientation. The bolt spacing is the same, it's jsut rotated. Try to mount up a WRX setup, and camber plates point towards the center of the radiator. Swap the left and right hats, and all of a sudden they're only slaned ~10 degrees, meaning you just get a hair less caster if you're running the plates all the way negative, which most will never do on a street car.
So, why a WRX setup instead of a GC, or unobtainium JDM Legacy setup?
Easy. Selection, price, and common weight. I've got a set of Flex's designed for an STi. An STi weighs about 3300 pounds. A WRX wagon weighs about 3100. My wagon weighs around 3150-3200. You can see where I'm going with this. It's even better on a sedan, but, in my experience, with a fully loaded car (and I'm talking about ~1300 pounds not including my fat ass), the car barely sags, is still controlled, and doesn't get saggy wagon butt. You can barely tell it's loaded. Yet, becuase the spring rates and damping are designed for a car of the same weight, the handling is so improved it's scary. Ask any of the guys in my local club with WRX's who try to either pull away from me in twisties, or try to keep up.......there isn't a car Subaru makes that has better wight balance than a Legacy wagon, and you better beleive it makes a difference. Additionally, WRX coilover setups are all over the used market; I got Flex's from a friend at the market rate of $1000 with about 3k on them because he got an '05 and needed a new set. Compare that with AGX's for 500 (charitable), decent springs (250) and Group N tops to prevent pogo, and to me it's a no-brainer if you're concerned with making the car handle instead of just looking good. You adjust ride height without eating into available travel, and you get a much better damping setup than an adjustable strut that has to work within the confines of stock springs and god knows how many different aftermarket setups.
Issues with fitment, that you'll run into with any WRX coilover: The Legacy front suspension is a bit taller, so to get the same ride height you have to raise the coilover quite a bit; this means that almost any WRX coilover even at it's highest setting may not be able to get to stock height. If you're lowering your car anyways, this shouldn't be an issue. Corollary to this is that there's less hood clearance above the strut tops, because the shock towers are higher. Shouldn't cause an issue for any mechanically-adjusted coilover, but the electronic setups may be too tall once the motor is bolted onto the top (Tein Flex w/EDFC, Cusco Zero-2E, etc.) I test-fit and fund that it was too close for comfort, but it takes me 30 seconds to adjsut all 4 corners in a wagon anyways, so I don't really care. Electronic adjustment jsut aids setup on sedans, you're not going to change it once you get it dialed (at least in my experience)
I've also run Ground Control setups on both WRX struts and GC V5 struts, and can offer some advice if anyone's thinking about going that way on spring rates and free lengths (a friend of mine, who I used to work with at a shop, is the guy that did all of GC's kits back in the day, so I've got a pretty good grasp of what rates and lengths to use for specific setups. That said, my recommendation for someone looking to run a GC setup is to save your money and get an integrated coilover system: Tein Super streets are cheap even new and will be worlds better and quieter.
That's my 2 cents; take it, leave it, put it in your pipe and smoke it, and feel free to ask away if there's anything else you're curious about. I've been doing performance work with Subarus for about 4 years in additiona to monkeying with my own beast, so I can probably help
