What's the GPU hardware that is affected and not affected? Maybe it's specific to particular models/vendors.
Thant a lot for reading this and trying to understand the problem, much appreciated : )
I've now done the sqiddster test on 4 different laptops, all are giving nearly the same results with different brands (ATI, NVidia or integrated graphic cards). Also, I'm working on the game for one year and a half now, with more than 200 playtesters, and i've seen the game running on many, many computers. If the game fails to run at 60fps, it never runs with a "smooth" frameskip like the one we can see with the CPU throttling. Again, most of the time, as soon as the game reaches 45fps, it's very choppy and no more enjoyable.
Both Airscape and Penelope use WebGL, aren't these two tests relevant to you? (no bad intentions behind this question, that's a real one)
I'm more than ok to run new tests on different computers, but I really think we'll get the same results: on non-gaming computers, if the game is heavy on the GPU, the frameskip process doesn't work that great.