That's odd - you're right, Opera seems choppier with the Construct 2 version.
However, in all other browsers, the C2 one runs a lot smoother than the GM one for me.
I'm not sure why either happens - both javascript engines appear to use the same mechanism to draw the screen. So I'm not even sure if it's a problem with Opera - even if we changed it we might end up with the other browsers not displaying so smoothly. Opera have about a 2% market share so I'm tempted to leave it - the big three (IE, Firefox and Chrome) seem to run it just fine...