That's totally untrue, please don't spread misinformation about things you know nothing about. Even ugly horrible OO code is not inherently slower than beautiful code.
2. Ogre is harder to learn than both DirectX and OpenGL and the performance is horrible from the object oriented design.
I've not used Irrlicht but looked at it alongside Ogre when starting a new project and Ogre was the winner for us. It's not particularly difficult either.