First, a intercooler is a must, with any turbo setup. Especially for a custom job on a car not designed for one.
Second, pretty much all oem turbo's are designed for quick spool at the expense of upper end power so the WRX turbo is no different. Though the WRX is not as quick a spool as I'd like, it's not bad.
I had 185lb/tq at 2700rpm and 211 at 5100rpm at the wheels in 4th. At that point the tq drops off to the 6500rpm redline and 144 wtq. For Hp at my initial full boost rpm(2700) I have 86whp. At 4000rpm I have 155whp, and at my peak tq rpm I have 199whp. It stays above 190 whp until 6200 then it dips down to 185whp at the stock 6500rpm redline. Stock WRX turbo, 9 psi and full 3" exhaust. Soon as I get my new motor in; this is what I'm gonna run untill I get both cam gears and head back to Streetflight to get the chip fine tuned.
It doesn't seem to me to choke much at the redline. As for how it would rev to 7000, I'm not gonna rev it past the stock redline so I don't care. The stock Zetec is not a high rev engine and doesn't really breath well with stock cams anyway so if you do get a bigger turbo it will still drop 20 to 30+ hp from it's peak to the redline anyway. You look at most dyno charts of stock Foci turbo setups and you'll see mild to big drop offs past 5500rpm.
The only problem with a stock WRX turbo is the funky turbo manifold will limit your upgrade options to costly WRX upgrades. So if you're content with just 9-13 psi and 200-220whp max, the WRX is ok. Make sure your exhaust and downpipe are at least 3", cause that will make the engine breathe easier.