Linux. :P
Performance differs between Linux and Windoez because Windoez Pre-loads common applications in to RAM, however the drawback for this is you have less ram to do other things so although it appears faster, your really just running loaded applications out of the RAM which in most cases does have a faster transfer speed than your Hard Drive.
Linux does not pre load apps in to Ram, but this has an advantage. You may have to wait a few more seconds for your application to load, but compared to windoez your application will run allot smoother. This i have seen by running the labour-intensive 3D application Second Life. On windows it typically runs more choppy and 'Lags out'
Running this application on the same PC using ubuntu ~(With nVidia Restricted drivers) the application runs far smoother and frame rate is allot higher even in situations where it would suffer lag running under Windoez.
PS. What is yoru network card? Chipset and all. You can find this out by typing
lspci
in your terminal and searching the list for any key words relating to Network