500-1000 yards = 1,500 to 3,000 feet.
Impossible to really tell what you're facing, basic plane shape could be easily distinguised.
109 variants were very subtle, usually abulge there or wing extension.
190 variants, the D or "Dora" was easily identified with a long nose (LangNase)
P51 variants: one is silver, one is dark green
Spits...well thats hard to tell sometimes