I thought the halfway between F2.4 & F2.8 looked best or even the F2.8 but my personal taste is a little on the dark side.
The reason the curtain is still in focus when the iris is open is because you have to zoom right in to get a shallow depth of field with this sort of lens your camera has. This would mean you would have to get you camera further back which I know is not easy for you. Also if you do move the camera back and zoom in you may have to adjust the iris again as this will make things slightly darker.
Hope this helps Bob.