My understanding iz ZMQ is a messaging/rpc mechanism while
WDT is aimed at large data transfers (though it also works well with lots of small data as it's streaming)
Also I don't know that ZMQ uses multiple streams ?
bittorrent is optimized for sending to many and across peers.
for fastest data transfer the time it takes to read the data is the bottleneck once the network is optimized, so hashing before sending would be more costly (for a 1:1 copy)
we are considering 1:many case for future development but there are tools (like bittorrent) which already excel at this
Facebook internally use SDN which hashes source host/port destination host/port to pick paths. By using multiple connections on independent ports we do get multiple path utilized and can thus get better reliability and throughput if some are less healthy than others.
http://udt.sourceforge.net/ is a solution using UDP but we decided that TCP with multiple flow was a better tradeoff for us (not to reinvent most of the window, congestion control, etc... of TCP)