eh, if your going with the 5T's, I would recomend that you at least go with the 5 series center channel. For movies, most of your sound comes out of the center channel so I wouldn't skimp on it. It will also sound great with the 5t's. I'd be afirad that the 5T's would easily out power the 4C center and it won't sound as great or smooth.
Again if you can, I'd at least go up to the 5 series center channel. But as AcuDefTech said, you can get the 4C center to see what it sounds like, and if you think the 5T's are overpowering it, send it back with the free shipping and get the 5C in there.
I can't comment on the Def Techs since I don't know too much or listend to them really