The speed difference is around 50 times. In NAT mode I'm limited approximately by the bandwitdh of my network. Besides, network performance in bridge mode is worst when using SMB/CIFS share than when just surfing the web.
Performance considerations
In the next article from this series – ‘Bridged Networking in VMWare’ – I will explain why NAT networking requires additional overhead comparing to the Bridged. It should be said that on an average system this overhead is insignificant when transferring from the external network to a Virtual machine. However, port forwarding works considerably slower. In my tests maximum HTTP transfer speed with port forwarding was approximately 60 Kbytes/second when downloading from a VM to an external machine. Transferring in the opposite direction using pure NAT w/o the port forwarding was done at 11 Mbytes/second. The physical NIC operated at 100 Mbps speed.
If you are planning to use NAT with port forwarding for internet services, host only networking and native OS NAT is probably a better solution. On Microsoft Windows Server 2003 NAT is configured through the “Advanced” tab of the physical NIC properties. You would need to check the “Allow other network users to connect through this computer’s Internet connection” checkbox and select the VMWare host only adapter in the appropriate drop-down list. By default the adapter is called “VMware Network Adapter VMnet1”.
The Windows native NAT gave me full NIC speed when transferring with the port forwarding.
http://communities.vmware.com/message/415551
"sudo ethtool -K eth0 sg off rx off tx off" fixes it; adding "tso off" gives "Operation not supported", but it works fine without.
http://geekinside.org/drupal/node/475/edit
Linux add ethtool duplex settings to a network card permanently
http://www.cyberciti.biz/tips/howto-linux-add-ethtool-duplex-settings-pe...
Ethernet connection slow when vmware has its own nic? (Ubuntu as host)