Look buddy. Welcome to internet forums. Not everyone who posts has first hand knowledge of what they are talking about. Did you build and/or drive that sub 8 min lap STi... didn't think so. What we are all doing is sharing what we know, or have heard and feel is creditable. Sometimes we are wrong, sometimes not.
BTW, is the STi in question using a VF36 or VF37, or is it some other turbo that happens to be a twin scroll. BTW, when you say fastest that is in one arena. Is that same car the fastest drag Subaru? Probably not.
I'm sure there are a good number of upgrade turbo available in a twin scroll configuration. Of course there could be a car out there that runs like a bat out of hell with such a turbo.
What I was addressing was the original posters desire to run a twin scroll, without explicitly mentioning his goals. If he is into drag racing, he might be better served with a HUGE turbo to bolt-up to the stock plumbing. If he wants a turbo with fast spool-up and can settle for around 300 whp, then a twin scroll would be a fine option. All I'm saying is that it's not a panacea or the best answer to every question.