I have use my "newer" macs 8500/7500/840av/950/IIfx to make 800k disks for
my IIgs and have noticed that the auto inject 1.44 drives use on the older
systems (IIfx, 840av, 950) have no problems making disks that are readable
on the IIgs while the 8500/7500 non inject floppies cant do it reliably.
So your better off using an old quadra to make 800k disks for older
machines. I have no idea about writing 400k disks because I dont have any
machines that use them.