Also be aware that a rear projector on the
cyc or
scrim will have a spot which you can see a 'hot spot'. Depending on what and how you are projecting, you can get rid of it by actually blocking the 'hot spot' with a piece of wood. Just have someone stand in front of the cyc and say when they can't see it anymore. This however might lower intensity and possibly block images. Also depends on how bright projector is too.
Is front just not an option? When I was orginally planning for Ragtime, we were going to do 2 rear projectors with .8 lenses. Instead, we ended up doing front with one, more powerful projector. Also gave us more stage space which the director kept whining about.