I recently bought some Atlas O... mostly new and some used ...and did some testing.
I put my volt meter on the binding post of my Lionel transformer (ZWL 6-37921) and brought it up to 18 volts. I grabbed some old speaker wire that was within reach and hooked up each section of track and got the following results.
New Atlas O = 17.85 volts
Used Atlas O = 17.85 volts
Used Atlas O (center rail with Black Oxide removed) = 17.85 volts
Used Atlas O (center rail with Black Oxide removed & then coated with NeoLube No. 2) = 17.86 volts
Old Super-O = 17.92 volts
I guess I will use the NeoLube No. 2 to touch up the used Atlas O that I purchased. It's incredibly easy to apply and indistinguishable (at least to my eye) from the center rail of the new track... so, I'm not going to bother trying to touch it up with *gun blue*. If I remember I'll report back in a month or so on how well it wears.