I've never heard the 4C though that is what is recommended for that room size usually. I just went with the 5C because the 4C was backordered.From what I've heard the 4C is a pretty great speaker too.

The 606 msrp is only $600 I think... the 607 (the 2009 version of the 606) is only $515 here. And if you spend $450 on speakers you get $75 off so it would be $440. You may find the 606 cheaper than that, but $680 is definitely way too much.

The 4T Hybrid SD ($1569) + the 607 ($440) would be just $9 over your budget