I read about the Olympus OM4 and Pentax LX and found in their technical specifications that they can go 240 and 125 seconds respectively. After I acquired both, I found out that the OM4's 4 minute limit is hard coded while the LX will go on for as long as it takes to properly expose the scene - while monitoring it in real time and changing accordingly, or the batteries are depleted. Certainly a good argument for not strictly relying on the spec sheets!
Do these cameras also have a facility for reciprocity? I imagine that could be quite bad without one.