After Upgrading my iPad 3 to iOS 6, i experienced a very slow and unstable wifi performance. This is my hardware setup:

• Router: Linksys WRT54G/GL/GS
• Router – Firmware: DD-WRT v24-sp2 (07/21/09) std
• Apple iPad 3 32 GB 3 G Model

The problem was the wifi standard mode – the router supports the standards 802.11b and 802.11g and offers a “mixed” mode, where devices will automatically choose the right standard. The mixed mode caused the problem, changing the configuration to “g-only” fixed the issues and wifi works as expected again.