What are the key differences between the Canon 580EX II and the Canon 600EX RT?

The key differences between the Canon 580EX II and the Canon 600EX RT are that the 600EX RT has built-in radio transmission for wireless flash control, while the 580EX II relies on optical transmission. Additionally, the 600EX RT has a higher maximum guide number and faster recycling time compared to the 580EX II.