The most important spec for the modern Subaru enthusiast is that the Corolla GR is rumored not to be able to fit two car seats in the back. For the Subaru fans out there, I'd probably skip the GR and just get a WRX. Think of how important the legendary Subaru AWD system is going to be when you are in the Walmart Parking Lot when there is a half of inch of snow on the ground. It just makes sense. The GR just isn't practical.
And if you aren't looking for practical, the the GR isn't for you either. Think of how many people you could impress if you bought a Mustang instead. It's basically a rear-wheel drive WRX. It's got that massive curb weight that you know and love, and you'll have the ability to say, "I own a Mustang." Saying, "I own a Corolla" doesn't have the same appeal.
Think about it. And stay away from the Toyota dealer.