VIA GbE driver (VT6130/6122) for ESXi5.1
This version is based on my own driver of ESXi4
And, plus bug fix and extra patch with iSCSI optimized parameters for istgt
You can get best performance with istgt. The istgt is integrated in NAS4Free
Also, the package is available on openSUSE, Debian, Ubuntu, NetBSD and FreeBSD.
net-velocity-1.14-p2.x86_64.vib is here:http://shell.peach.ne.jp/aoyama/archives/2160
In short, maximum read is over 100MB/s, write is 78MB/s by VT6130.
Try it on your environment.