I don't know... I upgraded from an i7-970 (3.2-3.4 GHz) to an i7-4820k (OC 4.3Ghz) and added a SSD and am seeing a HUGE difference in FPS / smooth gameplay; it's staggering really.
Of course, I didn't upgrade solely for this game, but it was a pleasant surprise to see such a positive performance impact here.
I too would like to see a response on the "blade of grass" thing. Please post a video of this phenomenon, or at the very least, please describe in detail where this happens. I'd like to go verify its existence.
This game is an absolute blast, in my opinion. Like the poster above, I haven't lost this much sleep playing an MMO since, well, since I played Warcraft at launch. It's nice to have that feeling again.