Are you wanting a cab style cage or a full cage?  Since you don't plan for passengers in the back I would suggest keeping the weight to a minimum and just doing a cage in the cab.  If it was designed to work with a full cage you could have that added when and if you wanted/needed protection in the back.

Cage plus tall guy equals bumping of head.  I'm always entertained to watch Zembalayan fold up into his 4Runner when we've been in Moab.  Between his cage and CB radio it's a NASCAR style squeeze to get in.

My biggest opposition to the cage is that I don't want to keep my 4Runner as light as possible.