Is there any chance for a --march / --mcpu pair for intel core(duo)?

I'm currently running gentoo linux on a first generation mac book pro
equipped with a intel coreduo processor. Gentoo installation guide
states that --march=prescot is the best choice for my cpu.
But there are also some guides stating that --march=native would result
in better usage of the coreduo's features.

Left with this I was hoping for a intel core cpu-target in gcc 4.3
(which only seems to support core2..)

Is it even possible to fine tune for core(duo)?

Thank's in advance

René

(Sorry if this question was asked before - I searched the mailing-lists
and bugzilla without results.)