You can do all of this with a 4/3 sensor coupled with a s35lens, just with a cropping factor. The 4/3 size will give you the exactly same high quality image quality as a windowed 5k. A 4/3 sensor, would do 99.999% of everything you need, and could be a financially viable option for RED. The 3k IS NOT!
If A director calls for a 80mm lens wide open from experience he will expect to see that lens do what he knows that lens will do and that will only happen if that lens is mounted to an S35 sensor.