Really? A friend of mine had an HKS 3037 on his Evo IX with a shitload of boost and made just under 400hp, but i haven't seen many cars making much more than that unless it has a built/stroked motor. As for the engine note, i think they sound pretty badass, especially with a set of cams.
My brother has a IX with some nice parts on it (suspension and big brakes) It's awesome to drive and the responsive motor + sharp handling is phenomenal. We take both cars for a quick blast sometimes and, through the twisty stuff, the Evo is much better no question. The GT-R is able to keep up enough, though, and when there's a sweeper or open section, the GT-R can reel the Evo in quite easily. Both cars are tuned with light power mods.
Have to agree with Iron Chef and Eugene. The GT-R is far more satisfying to me. It's a special car to own and a privilege.