> symptoms.  Some have suggested either increasing number of nfsd's to 300 
> or greater, or abandoning TCP altogether and reverting to UDP, which 

4-way... I've heard (sorry don't remember source but it was found via google)
you should limit yourself on linux to max 8 nfsd's per processor, that would
mean 32 processes for 600+ mounts.  Yikes.  We have about 15 mounts per
server process, 8 processes per processor, also gives poor yield.  We're
migrating to a SAN with GFS to "solve" this issue (among several other
issues).

Is your server's network card stable and not saturated?

> 3) will change mount options, remove bg, add noac,rsize=32768, wsize=32768

32768?  Do you have the networking equipment to handle that without
fragmenting?  Are you already using jumbo frames with your 8192 packet size?

Good luck,
Dan W.