I have a similar sized room and sit 12' from my TV.  I have 4T's for the fronts, 4B's for surrounds, a 8D sub and 4C center.  The sound is phenomenal.  I would go with the 5C if you can swing it. I would have but just couldn't shoe horn it into my space.  The 4C is perfectly fine, but I think the 5C would match a bit better with teh 4T's. 

You really want to try and keep the front and center speakers on the same plane if possilbe.