P2P and C/S, is it possible to determine which one is more bandwidth consuming?
One would say that P2P is better. But in reality, you cannot tell by the information you provided.

For instance, the bandwidth depends on queuing delays. Therefore, assume that one of the nodes in the P2P network has a very small queue (or overloaded), while our server is super powerful and its queue is hugly big ! Similarly, it depends on the latency of the nodes. 

It depends on the bandwidth of the channels in the network. 
It depends on the round trip time.  Therefore, P2P peers may be very far away from each other ! (China, Iran, Venzuela for example). etc ..