I have not driven a 2011 STI, but the 09 STI I drove felt stiffer than the 2011 WRX I purchased. The 2011 WRX is very stiff in its own right though, there's no doubt that it is a performance car.
As far as differences go, you pretty much nailed all of the major ones. I'm sure you can order an STI wing through subaru at a later date if you really wanted to. I will say that I love the look of my 2011 with no wing.
If it's a daily driver I think you'll be more satisfied with the WRX. If you're looking to race or autocross, maybe the STI. Either way, you'll have a car quicker than your G37s for probably cheaper than your G37s...albeit giving up some luxury.