the core on the 1500 dollar intercoolers is practically twice the size as the greddy, and the greddy requires hacking the bumper beam, whereas the aps, i know from my own purchase, comes with a bolt on beam..also, the piping diameter is different, so i hear.... if you are that insistant on the t3/t4 setup, DO it! it would be sweet, but you would have to turn the intake piping, around the intake i would assume, the oil and water feed and drain from the turbo would change, and simply put, could be a pain in the ass for a daily driven car.. basically it seems like the exhaust systems are similar.. the hks carbon ti is "pretty" the evo is quiet, but the price difference is up to you. If you want other stuff, buy it.. and if you do a t3/t4, you have to take me for a ride!
~ mark
*i just remembered ~ there are different turbines available for the aps turbos, mainly the 40, and the 30.. look at
www.aps-wrx.com
besides, the australians have been making power with wrx's for years, reliable, strong, and most of the time, lots of power