A rooted and streamlined Evo cannot compare to a rooted and streamlined 3vo.
Using CF Bench, the only CPU-side benchmark that really makes things obvious, I'm able to just exceed a stock SGS2 when I overclock on demand to 1.5 GHz. Nothing you can do an Evo will put it in that territory (and some fans are overclocking the 3D to 1.7 or 2.0 GHz, when the individual phone allows it).
I hear the Sprint SGS2 is coming soon, but the rumored date keeps changing - Sprint is definitely getting a copy.
Most of my friends in Europe with the SGS2 _really_ speak highly of them, although one just couldn't find the dual core advantage for his particular uses, so he went and traded with a buddy for the Nexus S and is actually happier with the performance (available as the 4G model for us on Sprint) - so, everyone's mileage and preferences varies.