Eh, running in pio-mode won't help your performance ...
I copied 36.1 GB of data in slightly less than 9 minutes for 71 MB/S
client: windows vista 64
server: openbsd amd64
kern.bufcachepercent=40
samba
socket options = SO_RCVBUF=65536 SO_SNDBUF=65536
em nic, 4K jumbo frames
ahci0 at pci0 dev 17 function 0 "ATI SBx00 SATA" rev 0x00: apic 4
int 22 (irq 10), AHCI 1.1
sd0 at scsibus0 targ 1 lun 0: <ATA, WDC WD10EADS-00L, 01.0> SCSI3
0/direct fixed
switch: hp ProCurve 1800-24G