4th and 5th axis isn't really a concern for the base machine. There aren't any commercially available systems for these size machines I am aware of, so you will probably be looking to build your own 4/5 axis for either option. If you are serious about 4th and 5th axis, you will want to pick your controller hardware/software carefully.
The G0704 is certainly a well documented and well supported conversion, not that the PM machine isn't, but the G0704 has years of knowledge (threads) behind it.