Ah, I should note this was with Steam overlay/FPS counter/etc disabled too, like they recommended, so that couldn't be the cause of this.

I tried testing it against my legit Steam copy, could only get up to the first menu/sign-in screen though, but even there the new Denuvoless EXE seemed to have a huge performance increase: 180-200FPS Denuvoless vs 110-120FPS legit Steam. Really hope someone will do a proper comparison soon.