Well, I see it like this. JMO--- You may not be able to tell a significant difference in a room of your size, especially if you get the 12D, The 5T's paired up with the 12D would definitely fill your room with room to spare. But the 6T's are awesome speakers ( never heard em, but were rated in top 10 of CNet's audiophile speakers, prestigious award there), so if you have the budget, than get the 6T's, that way you'll never wonder what if.......... but whatever you choose, you will be happy. I know I am. Good luck. Let us know what you go with in the end. And I say get the 6C, especially if you watch movies a lot, it's a good center, one of the, if not the best I've heard. That's what I have, and it's my favorite speaker.

Browninggold, I gotta mancrush on your setup. To say I'm jealous would be a vast understatement. Nice work!