(weaveworks person here)

If you check out the PDF that fons posted above, http://rp.delaat.net/2015-2016/p50/report.pdf, then you will see pretty extensive testing showing that Weave Net, flannel, and Docker Networking have similar VXLAN performance for unencrypted traffic. In all cases, it is good enough. Alas the testers were unable to get Calico working.

The question is: when do you want top performance for encrypted traffic? Most of users want encryption for the wide area or public cloud, and when they can't use a VPC. Our solution is pretty good for these cases. Obviously at some point we'll enable IPSEC too.