Need help keying a wedding veil

Hello, Creative Cow people :)

I've got a lot of green screen shots to key out and I'm making good progress but I have an issue with one of the shots. It's a midshot of an actress dressed as a bride in front of a green screen. The problem is her veil. I've managed to key it to a fairly decent level of transparency which doesn't look at all bad when viewed in a still frame but when I run a RAM preview the semi-transparent areas are really noisy.

I've resorted to the making the veil fully opaque which I guess is the way it'll have to stay unless someone can help me, but it looks kind of dirty (because I've colour corrected it to look like an old photo) and I know I'd impress the socks off some people if I can key that veil properly, and that might get me a job somewhere down the line which would be awesome :)