The biggest issue with DSLR projection is artifacts. Our 5Ds ignore most of the light infrormation gathered by the sensor when recording motion. This line skipping--combined with a relatively weak codec that doesn't record individual frames--means any rapid or complex motion will turn to mud (messy pixels, loss of detail, etc). Then there's the moire that pops up with fine textures like wood or fabric.
What might not be noticable on a computer might become garish on a massive cinema screen. Waves, for example, look just fine in camera but look awful on larger displays.
By contrast, Red footage is mostly free of such artifacts. When you downconvert your 4k footage for 1080 projection, 4 pixels are combined into one, further reducing digital errors and improving color rendition. Or so they say.
On the other hand, the average audience might not even notice DSLR artifacts. A strong story, and all the minor issues don't even catch the eye. One thing i'd be careful with is bright flashes that dominate the frame (like photo strobes). The rolling shutter will reproduce a flash that only shows up in 1/3 or 2/3 of the frame.
I've seen 5D footage on a 25' screen that looks amazing, and I've seen footage shot with the same camera that shows all the hallmarks of poor digital acquisition. If you're aware of the limitations, you should get away with it.
Good luck!