I am currently migrating to ESXi and all is going well so far apart from this one rather odd issue...
All of my vm's get near perfect disk speeds locally/via the vsphere console (Around 100MB Read, 90MB write on a single hdd) however the second I try and copy any files over the network, I get 11MB/s both ways. I have gigabit lan all round so the limitation/issue is something to do with ESXi it's self from what I gather.
I am running the latest version of ESXi on the server and vSphere on my work station and all VM's have the latest VMware tools installed.
VM -> VM = 30MB/s cap
VM -> Physical = 7MB/s Cap
All servers running server 2008 R2 either Standard or Enterprise, All clients running Windows 7 pro or enterprise with 1 mac (running El Capitan 10.11) on the network which also suffers
How does your setup compare to the one posted in that reddit link?
VM to VM should be much faster, what NIC are you presenting to the VM's? E1000 or VMXNET3?
If you're thinking that it could be disk related, have you checked the output from esxtop?