I think the problem hasn't been the hardware, I think the problem has been Flash itself. It's poorly designed and written software. You might look on the net for the trick to get YouTube to use HTML5 instead and see if H.264 runs well without Flash slowing it down.
So what level of hardware (and expenditure) do I really need to get smooth,
full-screen, HD playback of flash video? (I've been chasing this since the
90's, and the answer has always been MOAR!)