In Michaels tests, the HD6450 he used stands out as a candidate for being gpu bound. Yet, despite that its results were pretty much dismissed, it too showed a range of roughly a 1.5-9% improvement. There have been numerous articles over the years which highlight small 2% type of performance gains brought about by newly enabled feature xyz. Alone, their not much (and especially when they may pale in comparison to 60% type gains seen on other devices, in such a case like this), but they compound well enough. But I digress. The point is, I'd suspect that there are some gains to be seen on some of the higher end APUs. Similarly, I'd suspect that a Iris Pro would see some improvement too (did Michael look at that one? I can't remember such mention).
Though, at this point, I not clear if the cpu governor change is only impacting Intel platforms or if it extends to AMD too ... someone pointed out a commit related to p-state and Haswell in one of the threads.