@dburne, definitely go for the center mount with extension. Not only is it more realistic (unless you're flying an F-16), but it is much more comfortable and I find it much more precise as well. An extension should fit the adapter either way (joystick, adapter, extension, grip or joystick, extension, adapter, grip).
@rrohde, will the base be available without the vkb grip, just an adapter and base?