Setting vfs.nfsd.srvmaxio in Tunables

[scottrus71]

I'd like to attempt some NFS tuning by setting vfs.nfsd.srvmaxio to increase wsize and rsize. From the FreeBSD 13 release notes there are some restrictions:

A sysctl called vfs.nfsd.srvmaxio has been added that can be used to increase the NFS server’s maximum I/O size from 128Kbytes to any power of 2 up to 1Mbyte. It can only be set when the nfsd threads are not running, and will normally require an increase in kern.ipc.maxsockbuf to at least the value recommended by the console log message generated when setting vfs.nfsd.srvmaxio is first attempted. 9fb6e613373c

To ensure this is set before nfsd starts up, should vfs.nfsd.srvmaxio be a sysctl or rc.conf value in System -> Tunables?

How can I find the recommended kern.ipc.maxsockbuf size when setting vfs.nfsd.srvmaxio via System -> Tunables?