Traffic to/from the rest of the chassis is (I recall) via two 40 Gbps fabric channels (for a 65xx-E with Sup-2T). I.e. half the ports use one fabric channel, the other half the other fabric channel. (To obtain the 80 Gbps, you need to balance traffic across both fabric channels.)
I don't recall what the architecture supports for traffic between ports on the same C6800-32P10G line card.
BTW, I also recall (?) many DFCs cannot guarantee wire-rate for full fabric bandwidth if using minimum sized (64 byte) Ethernet packets.
The 32 port card has two DFC4Es (one per half the cards ports?), each rated at 60 Mpps (IPv4). 60 Mpps guarantees about 40 Gbps (for minimum sized Ethernet packets).