Microsoft Research released a new Network Speed Test App for the Windows 8/8.1. This app can test Download/Upload speeds of your Network, This application supports both Windows 8 PCs and Phones.
Features
Measure your network latency, download and upload speeds.
Understand what activities, such as streaming music, you might be able to do.
See information about your network, such as the SSID and BSSID when you are connected to a Wi-Fi hotspot.
See your past network performance history.
This application uses 14 seconds, so the higher the speed of your network the higher will be the data usage. On a 2Mbps bandwidh it will use 3.5MB of data while on 10Mbps it will use 17.5MB. You can read the calculations and other details here on Microsoft Research Page
You can get it from Windows store.
Windows 8 or Windows RT
Windows Phone