The 400 f2.8 is the stuff, for me anyway, that dreams are made of.This stuff is currently used in Nikon's new 400/2.8 and the new TC14EIII.
If I sold all my gear, I'd be about 1/2 way toward being able to afford one. But then I wouldn't have a camera to use it on.
So I won't torture myself by hitting the link you posted.