Every thing I have ever read/seen about the STi vs EVO (pretty much any version of either) has said that the EVO handles better. Mitsubishi is one of the world leaders in suspenson technology.
You have obviously never had the pleasure of riding around in an Evo 7 GT-A. Make sure to bring lots of barf bags if you do...
I've heard lots of people say that the Evo's handling feels
better, I've not yet seen any reports outside of Japan with numbers that say it actually performs
better. I'm not surprised at all on the feel-better factor - a stiffer suspension setup and faster rack combined with slightly larger tyres will have it's impact. I also think that while that will make some people happy, there will be at least as many others that will be happier with the on-the-road feel of the STi in non-track conditions.