Well, even a stock length tightbore will slightly increase the fps output, due to higher compression, but I'd think you'd still be under 400.
As for buckings, I usually just use Systemas, as they're cheap and usually work pretty good. Some like the Guarder clear buckings, but they seem hit or miss depending on the application. Prometheus buckings are supposed to be awesome, but the one time I had one I happened to also have a faulty barrel, so I never reallly got to test it. I've also heard a few people say they caused feeding issues in their guns, so I guess that's hit or miss as well. Another one that's supposed to be good is the firefly bucking.
But like I said, Systema buckings are usually pretty good, and cheap.