As promised, Microsoft today released the System Firmware Update – 7/16/2014 for Surface Pro 3 users to fix the WiFi performance issues. _This update will further improve Wi-Fi connection and throughput scenarios. Surface Integration (v.2.0.1038.0) further enhances system stability. Wireless Network Controller and Bluetooth (v. 15.68.3042.85) further improving WiFi connection and throughput scenarios. Check for updates on your device. You can order Surface Pro 3 from Microsoft Store starting $799.

The rest of the story...
Microsoft News