samba - Apr 2005 - Samba not utilizing full available bandwidth

I recently upgraded a part of my network to Gigabit ethernet, basically 
between my Linux machine and my main windows machine, is now gigabit. 
The problem is that, and the whole reason I went with it, is to get 
faster speeds with samba. I've only been able to get 13.4 MB/s as a 
maximum transfer speed. I don't expect to be able to get 125 MB/s. If I 
use HTTP I can get around 18 MB/s, and that would be fine I suppose for 
now. Now what samba can do is, that I can get two connections to two 
different machines going at about 13 MB/s one and 12 MB/s (100 Mbps) the 
other, and they don't really affect eachother, so the bandwidth is 
there, but getting samba to send as much as possible down one connection 
seems to be a problem. iperf between the machines, managed to get 528 Mbps.

I tried fooling with the socket options, raw read, and and max xmit 
values in smb.conf

adjusting raw read, and max xmit just make it alot worse, I've settled 
on the following socket options as being the best but they only get me 
13 MB/s as opposed to lets say 11 MB/s or 12 MB/s.

socket options = TCP_NODELAY, IPTOS_LOWDELAY, SO_REUSEADDR, 
SO_SNDBUF=4096, SO_RCVBUF=4096

SO_REUSEADDR doesn't seem to do anything actually, but the other ones 
made noticable difference based on what they were set to. So I'm sorta 
out of ideas. Would adjusting the MTU of my network help?

Steve R