Is the "TBB test" UDP? I'm not that clued up on this stuff but assume there may be less collisions with UDP and that's why it's faster.
UDP is faster because it doesn't care about packet loss or flow control, and also has less overhead in the actual frame than TCP.
Collisions happen at layer 1, physical, when a simplex connection has two transceivers transmitting simultaneously hence no usable message is received by the devices sharing that layer 1 network. UDP and TCP operate on layer 4, transport, hence make no difference to collision count. Errors can only propagate up the stack as they are encapsulated on the way down.
The TBB test is TCP. Port 8095 for single thread test, port 80 for 6 thread HTTP.