Pretty tricky to find solid evidence either way for that CPU.
However, over the past few years I have come to rely many times on Gentoo documentation, and once again, it looks like Gentoo Docs (or at least, Gentoo-related
) come to the rescue.
Check the link above; read down to the "Basic Installation" paragraph, where you'll see this:
Originally Posted by The link Above
CFLAGS="-march=i686 -mmmx -msse -msse2 -msse3 -Os -pipe -fomit-frame-pointer"
And based on that, I'd go with i686 as a safe bet.