The summary states it all. The preliminary gnome 2.18.0 ebuild requires gnome-speech 0.4.10, and it is also the version that comes with gnome 2.18 on the gnome website. I searched, and didn't notice a version bump request yet, so here it is.
Yeah I missed that somehow, that's why the ebuild is in the overlay for now. Thanks for remind me :)
Fixed in CVS, thanks.