SYN Flood detection - what are reasonable values

Some *practical* firewall advice needed from people running
with SYN flood detection rules..... what do you consider
reasonable limit and burst-limit values?  The classic textbook
values of 5 and 10 seem unreasonable as in:

-A INP_FLOOD -m limit --limit 5/second --limit-burst 10 -j RETURN
-A INP_FLOOD -j LOG --log-prefix "SYN-FLOOD: "
-A INP_FLOOD -j DROP

These just don't seem to work, especially with NFS active.  I'm
currently running with:

-A INP_FLOOD -m limit --limit 10/second --limit-burst 50 -j RETURN

But I'm curious as to what other people are running on their LAN
servers, especially ones running NFS.

Ian