I measured the springs diameter last night with calipers. The red spring is .445" and 9.25" in length, the black spring is .435". Could be the difference in paint? I was unable to measure the length of the black one because it's still on the bike and under compression for sag height. Maybe I'll have time this weekend to mess with it.

 

The stock spring from a 2009 (white) is 10.1 inches, if that helps and doesn't confuse things.
I'm now using the red spring from a 2009 SF. Seems stiffer, less preloaded yet not as saggy.
I might have more numbers somewhere. I'll look later and post what I find.