It depends on the browser. I see you've got 'Preview browser' set to Chrome which does not have a hardware accelerated canvas. It runs 50fps in Chrome for me, but still silky smooth 60fps in Firefox 7 and IE9, which both have a hardware accelerated canvas. It's also slow in Opera and Safari which don't have hardware acceleration yet either.
I think Chrome are adding hardware acceleration soon. Not sure about Opera or Safari.
BTW, you shouldn't use an opacity of 0 to hide an object - it still attempts to render the object, which takes rendering time, you just don't see anything. Set the object to invisible and it does not even attempt to render the object, which is faster.