Damn, I wanted to reply to this. Anyways, you pretty much covered everything I wanted to say.His main problem isn't his speed, he reaches 422 after a single Rock Polish. His main problem is the lack of a Fire or Ice attack to threaten other Grass-types, as well as floating steels (Skarmory and Bronzong). On top of that, he suffers like most other physical sweepers from Intimidate. This allows stuff like Gyarados and Salamence to switch in and survive Stone Edge, then OHKO with Fire Blast/Draco Meteor or Ice Fang, or switch out and lower its attack even further. A physical Hidden Power (not based on consuming berries; Natural Gift) would help with the former problem. Earthquake / Physical Fire or Ice / Stone Edge or Wood Hammer / Rock Polish would be decent, nothing OU material though.
Nothing feels better than having my hazards up with the sand blowing after setting up Rock Polish and dropping the Wood Hammer of justice on some unsuspecting Pokemon trying to defend itself 8D!