The Red footage was shot at 4K and downconverted to 1920x1080, which is the same resolution as the video from the DSLR and EX-3. Nothing is blown up in those charts.
The only reason you would shoot less than 4K on a Red is if you wanted to do slow-motion, in which case you would switch to 3K or 2K. By shooting at a higher resolution than what you end up with you get more detail than just shooting natively at that resolution. Most people who shoot on the Red finish at 2K, 1080, standard definition, or even for the web.
I'm about to do some pickup shots on the 5D for a film we shot on the Red. They take place inside a car and in low light, for which the 5D works well. On a previous project we shot some b-roll on the 5D of an artist's canvasses, and we got a lot of moire on the fine textures of the canvasses and pencil drawings. But our EX-3 footage of the canvasses turned out fine. Do tests before production under various situations, with different textures, etc., and have a DIT on-set checking the footage.
Focus pulling is an issue on DSLRs, so people end up either getting special focus pulling equipment for their still lenses or putting PL mount cinema lenses on the cameras. Also, the shallower DOF on the 5D (because of the bigger sensor) means that to get a useable DOF you have to stop down and add more light, unless you have an amazing focus puller who can pull focus on shots in which your focal plane is razor-thin. Or you avoid the longer lenses and compositions in which you get razor-thin focus.
BTW, if you are shooting on DSLRs, invest in PluralEyes. It will help you sync the production audio to the camera audio.