Where's your bottleneck?
I shot on a 7D for the first 2 years of my career. It said 1080, but it wasn't 1080. It wasn't really even 720. Then I got and hacked a gh2. My footage was so much sharper. But the dynamic range still wasn't there, and clients still had a hard time respecting a tiny DSLR. So I got the C300 at 0% financing. It totally paid for itself. My footage was even sharper, a true 1080, and with a good 12 stops of dynamic range. Worth it in every way for me.
Now, I had the benefit of working for 2 years with the 7D. I did everything I could to get it to look as good as it could. After those 2 years, the camera was the bottleneck. When I started out, I was the bottleneck. A better camera would've been wasted on me. I needed to learn to light.
That said, there's no reason to get a 5D when you can get a C100 for the same price. The C100 is so much better for cinema it's not even funny. Now, I have a Red Dragon and a C300, and if clients didn't still ask for the C300 specifically, I'd swap it out for a C100.