Is there a particular reason to get 400 fps? Since the regulart monitors are 60 hz, and more expensive ones get higher hz but it seems a bit odd to aim for 400 fps since no regular pc screen can display that framerate. They go up to 240 hz.
In any case, Minecraft is a very light game, so I think basically any AMD FX CPU with a decent overclock or Intel i3 or better CPU combined with a GTX 750ti or better GPU can get 400+fps.