I have the same issue, when opening new tabs the cpu usage for that tab goes up to about 40% in opera's dev task manager.
And when this site: http://www.reddit.com/r/amiibo/ is in focus the cpu usage goes up to 40% consistently. I have an intel core i5 with 6 gb of ram; running windows 10 TP 64 bit with hardware acceleration on in opera settings.