I have an m4000 with 6 10GB nics. With link aggregation. We have clnt_max_conns=1. If you have the correct drivers you normally do not need to tweak this. It is meant for a really fast system connected to lots of slower or very remote boxes (with lots of latency) to enable multiplexing. It handles the disparity in local response times. Like multipathing.

Try loading and then measuring:

Maybe the NFS traffic load across systems is not high enough to push the new connection(s). Or your code base is really well-written. Unlikely, I admit. Ours is awful.

So - artificially increase the NFS traffic by writing some threaded code that reads (or writes) many files at one time. Be sure to do something to avoid the effects of local file caching, or what you will really be measuring is not NFS TCP effects. This will not fly on a production box. You should have svc_t waits of 50ms+ (as a guess) if you are really saturating the connection/driver.

IMO, what you want to look at is iostat -xnmz 1 10 - svc_t time, %b, etc.
-- for NFS mounts. iperf is also relevant, BTW. It is a valid tool.

If your before/after change does not impact this kind test, you are wasting your time with the change.