If you want to leave large downloads uploading, and still use the computer for other things, such as playing offline games or ripping music, you can find your upload speeds crawl along because the FTP client is being slowed by other software.
To stop this happening, you can set your FTP client to have priority over the game or other software.
– Goto the Task Manager, then the Processes tab.
– Find your FTP process, for my fav FTP client Filezilla its Filezilla.exe
– Right click, and choose Set Priority
– Change to 'High'
You will need to repeat everytime you startup your FTP client, but its still handy as you can make the most of your PC without loss of speed.