It's not a 9% difference. The performance of the 1.1 is going to be similar to a 2011 Macbook Air, while the 1.2 exceeds the 2015 Macbook Air. If you think what you are doing would be okay on a 2011 Macbook Air, then go for the 1.1.
Really? The 1.2 GHz exceeds the 2015 MacBook Air? What have you seen about the 1.3GHz?