How about a .8 km baseline?
One of the projects on Mauna Kea is the OHANA project. The goal is to link about a half dozen of the scopes on the mountain to form an interferometer... the baseline would be about 800 meters... All these scopes are among the largest in the world...
The resolution of such a system would be mind blowing....
It is still in its very early stages, but it is progressing and has high priority... If it works it would ensure that Hawaii remains at the forefront of cutting edge astronomy for quite a while.