Problem solved thanks to the following :
added the option in /etc/exports on the serverside to 'async'
restarted services on the server in this order :
then from client :
mount -o remount nfsservernamehere:/home/shareddir
now it's steady at 21 Mb/s ! (100Mbit NICs in both server and client)
Posting this in case somebody can benefit...not bad problem solved in same day..
btw, remember that I still had the client fstab set to nfsvers=3