gcc Optimization settings for Athlons XP's (Gentoo users?)

What gcc flags are working for you guys? -march=athlon-xp is accepted I think...I wonder how it's different from just march=athlon.
Anyone gone too far and made things unstable or slower? Do these even result in a noticable speed boost for that matter?
I'm mostly worried about kernel compilation at the moment.

Here's a page containing all the GCC optimizations that are considered safe. They've been tested and shouldn't break any packages.

http://www.freehackers.org/gentoo/gccflags/flag_gcc3.html

The -march=athlon-xp contains SSE optimizations, unlike the -march=athlon.

-DarkArctic