PPG's are great. But AndrewTech has a lock on the American market, and their prices are less than attractive. Don't get me wrong. From what I understand they are a good company, and for sure they know Subaru. I'm trying to find another place in Australia that makes similar parts. I know there is no way most Australians are going to pay the kind of prices that AndrewTech commands in the U.S.
As far as PPG's and horsepower is concerned, I seriously doubt that any helical-cut gears in an 02 5spd. will handle more than 450 whp. Especially if you plan to slip the clutch now and then. PPG parts are probably about as strong as it gets, but the gears in the 5spd. are restricted in size by the size of the transmission housing. Given the space, you can do only so much to strengthen the shaft and the gears. A Dog Box is a whole 'nother ball game. But if you've ever driven a Dog Box . . .
Also, one dyno's 800 whp is another dyno's 600 whp. I'm sticking with Kito in Seattle, which is probably the most conservative Mustang dyno in the U.S. Not only does Kito know his stuff, his main Dyno man, Dom, is The Man, when it comes to tunes. Just my opinion, of course, but the guy who does most of the building on my stuff is a near genius when it comes to anything mechanical (he's a master mechanic who has done many builds) and he also agrees about Kito and Dom and Mustang dynos.
If I didn't have a wagon, I'd be shopping around for an STi 6spd. But I have a Wagon, and I love the wagon (more head room, more front window, and enough room in the back to put in my mountain bike, all my gear, and a quartered bull elk (it's done it twice).