Last night i looked at the grass anti-aliasing/shimmering issue. Grass is too noisy because the FXAA algorithm has no sub-pixel information. One way to improve the quality with a small sacrifice in performance is to use of MSAA2x, which renders two samples per screen pixel and then run FXAA on the result. The MSAA 2x rendering is very efficient, and more importantly, it provides a much better base for the FXAA. The result is that grass now looks more dense and the shimmering is supressed but not eliminated. The result is comparable to MSAA 4x, in some situations is better in some not but it is faster and less memory consuming. MSAA4x is able to completely eliminate shimmering but it doesn't provide AA filtering in some situations like a sharp texture patterns. It is more GPU and memory demanding, and its demands for more GPU power and memory disqualify it for deferred rendering in future.
I have to tune FXAA parameters for MSAA 2x/FXAA combination because in this case FXAA doesn't have to be that strong...
I prepared a few HD images for comparison. (click for full image...)
MSAA 2x + FXAA