[I thought I had posted this earlier, but apparently it was just saved.]
Reach4: The lip of the ceiling box is recessed more than 1/4" behind the ceiling surface., but no more than 5/8". The first metal extender you show is for a 4" box, the second is for extending a ceiling box something like 1-1/2". There are metal extenders for switch boxes which slide into the box, giving you just as much extension as you need. I can't find anything like that for metal ceiling boxes. Where I found stuff on the Web about people extending ceiling boxes, they were using those plastic extenders, which slide into the box. Either plastic ceiling boxes are designed different from metal boxes, or there's a major flaw in the design of the plastic extender box.
I will be hanging fans off the ceiling boxes. The screws will go through the holes in the ears of the plastic extender and into the metal box, where the former extends the latter no more than 1/2" to 5/8". I think code requires no more than 1/4" recess because of flame barrier considerations.
Jim: Yeah, I have no alternative but to notch the box to get it over the wires. Just very strange design for this, where you have to hack the box to get it to work.