My upper level - built on Mianne benchwork - has 3/4" ply (because I do climb on it) with a layer of 1/4" cork and then a layer of 3/4" ceiling tile.
The track is Atlas and is installed on foam roadbed. The layout is free standing and does not touch the walls in a 10'x12" room - but covers the entire room with a center "running/control" area.
I use Atlas track and there is almost no noise from the top deck. Perfect.
Thanks, another good suggestion. I love hearing about all the different methods people have used!