For posterity sake, I'll add some comments that might be helpful to those on the fence....
I owned an 07 STi that was basically stage 2+E85, some suspension and brake mods too, putting down 377whp/364wtrq. The car was a blast to drive. It handled well and sounded great. The sheer acceleration definitely surpassed that of the M3. I told myself that I didn't really care about the interior, the luxury and the prestige. After a while (108k miles), the ride was just too harsh, and the overall build quality was just so-so. I too was cross shopping an Evo X and an E92 M3. I test drove both and it was a clear win for the M3. The Evo just seemed so bland, nothing super special in stock form, and didn't really stir me like the STi or M3. The M3 is just....special. The build quality, well-rounded performance, looks, interior, prestige (if you're into that) sold me right away. Yes, if I were to mod the Evo I could make it into a beast like I did with the Sti. But it'll always rattle and never feel quite as solid or well-rounded as a daily driver and track car as the M3. For me, the selling point for of the M3 is that it's such a great balance of all the attributes an enthusiast would want in a car, plus the creature comforts as a DD.