Thanks for the reply, Paul!
All good questions and suggestions indeed.
Sorry for not mentioning it; I'm seeing the latencies over both NFS (over TCP) and CIFS. Actually, even a simple ping to the LIF shows the higher latencies.
At this point the "how did you measure latency over nfs/cifs" question is probably not relevant anymore, but I used both AIQUM and strace on linux (which shows the time it takes to open/list files).
I already did a tcpdump on the client's end, which shows no TCP retransmissions occurring. Or would you suggest doing the same on the controller's end?
I've got my 2 cents on the switch in between; So I'm also investigating that in parallel.
By the way, I'm running 9.7P6 at the moment.