I don't think splitting them up is a good idea. It would make things less obvious imho as you can have options that are not currently visible be toggled off. So, it could be you're on the Fill tab, set something there, switch to the Stroke tab, set something there, toggle back to the Fill tab and the user would be more likely to think "Hey, I set that option before, what happened?"

If there were three toggles, yes, but since there are only two in each tab, this would not happen.

The fill toggle would make the fill either always on top or always on the bottom.

Nothing you do to the stroke/markers tab toggle would change that, and vice-versa.

-C