Have you confirmed that it is not a samba share issue and is consistently the same across all kind of network traffic?
By the way, 2MB/s = 8 x 2Mb/s (not that it is satisfactory though)
I would take a look at these :
I would try these -
ifconfig # dropped packets? lots of frame errors etc.?
ping <any local device> # too much delay time?
sudo ethtool eth0 # to view current settings of the interface eth0
* Change the MTU value from default (1500) to 1492 or 1392.
* Change the link speed to 100 Mbps/Full-Duplex with the following -
Neither is very promising, but sometimes they help.
sudo ethtool -s eth0 speed 100 duplex full autoneg off