Question on NFS performance

[Valerio daelli]

Hi all
we have a FreeBSD 5.4 exporting some NFS filesystem to a cluster of gentoo boxes
(kernel 2.6.12).
Our exported storage disk is an Apple XRaid.
We have Gigabit Ethernet both on the client and the server.
We would like to improve our read performance.
This is our performance:

about 10Mb reading a file of 1Gb with dd

and iozone confirms this result.
We already use the normal optimization flags (we use rpc.lockd and
rpc.statd, on the client we have
read size 65536 and a read ahead of 4 blocks, the async options).
Is our performance the best we can get? Can we improve it?
Thanks for your help

Valerio Daelli