Quote - I'm willing to sacrifice quality for speed though...  But when I look at the videos "Samaritan" done with UE3 and "Infiltrator" done with UE4 it's easy to think there really wouldn't be much of a sacrifice, and a huge gain in time saved...

You'd have to sacrifice transparency. Most game engine techniques, such as deferred rendering, SSAO/SSPM only work well with 100% opaque surfaces. Multilayer transparency is getting better with the very latest hardware, but still is tricky to combine with other effects.

For example:

http://developer.amd.com/resources/documentation-articles/samples-demos/gpu-demos/ati-radeon-hd-5000-series-graphics-real-time-demos/

There's one demo showing transparency. There's another demo showing depth of field. I'm sure AMD would have loved to show off depth of field with multilayer transparency in one demo, if they could.