We commonly use Kino Flos for green screen. But your two 1Ks will work fine if you can diffuse them, and also scrim then down enough so that the screen is not too "hot" in relation to the foreground.
Actually, I'd be tempted to key with the 1K through a thick diffusion set well forward of the unit; probably add a double (red) scrim to the light; buy another 650 and light the green screen with the two 650s, and use the 150 for a back light.
That is, unless the green screen is huge, in which case having a couple of 1Ks to light it might be the better idea.
Rick Wise
director of photography
Oakland, CA
http://www.RickWiseDP.com
email: Rick@RickWiseDP.com
