Looking at the mobo datasheet, there actually isn't a slot 3 at all (I guess it's meant for a GPU).
So I have slots 6, 5, 4, 2, and 1 to play with.
Slot 4 and 6 are x16, 1, 2, and 7 are x8 (but 2 is physically x16). And it doesn't look like there's any lane sharing, they're all dedicated non-overs...