GI was actually used in that render, we just use suitably high settings. Not being able to see the results of your tests I can't say for sure what the problem is as there are several types of "flickering" that might be occuring, some caused by GI or other lighting issues, some caused by displacement "popping", some from aliasing, etc.
I would suggest changing your AA filter to Mitchell-netravali or even Cubic B-spline; results from the latter will be a bit "soft" but generally for animations you won't be able to preserve a ton of fine detail upon compression anyway, and sharp edges can result in artifacts and further aliasing. The AA filter can have a much bigger impact than the level of AA itself in many cases.
AA9 should be fine for most scenes, in fact it may be overkill. I think I used between 6 and 8 for the referenced mountain animation.
At any rate if you can show some comparative clips with accompanying settings or even just an image to show the kind of scene, that would help us give better, more specific advice. Motion clips would be best though.
- Oshyan