Yeah, I would use the 10.1 beta version. I did however have issues with my HD 4850 so I removed 10.1 from my gaming PC. It would be most helpful for my laptop, however I have a GeForce 8200M, which isn't supported by Flash 10.1.
You wouldn't notice much benefit with a high end CPU I would imagine, my gaming rig has a X4 940 @ 3.5Ghz so I didn't see any noticeable performance difference.
For something like my laptop, it can get fairly hot during flash gaming and pushes the CPU pretty good (AMD 2.1 Ghz QL-60). It gets even hotter while watching flash based TV and movies (hulu, netflix) and I really wish it would do hardware accelerated flash. If it was supported, offloading the work to the GPU would be quite beneficial for my lappy.
Flash does consume a lot of resources, but both the CPU/gfx cards you mentioned should be more than sufficient for Flash game play and video. One of our laptops has an older X2 and integrated gfx and it works just fine with anything up to 720p and I've never seen a flash game that ran badly on it (though it does get hot!).
Though you didn't ask about it, as far as video, I've noticed that flash performance seems to be heavily dependent on your screen resolution, as CPU usage appears to increase geometrically depending on how it is scaled, at least when I tried monkeying around with screen res trying to get better performance out of an old P4. But if you have the 10.1 beta and a supported gfx card any video should be fine.