I was looking at the scores from the Geekbench results (
https://browser.primatelabs.com/mac-benchmarks).
2.9GHz i5 CPU: 3761 / 7415
3.1GHz i5 CPU: 3821 / 7582
So not much difference in single core performance, but there's a bigger gap between the multi-core scores.
You are talking about 2%, meaning for instance:
- Assuming that you play videogames with your Mac, it would be 0,3 more FPS. Not worth mentioning.
- Assuming that you earn your salary with it, say you are a video editor, it would be 10" quicker in a 10' video rendering. Assuming that your price per hour is 200 bucks, it would take you 1.800 hours to earn that investment back. Basically after one year you will break even. Unfortunately by then the new model may be out and the depreciation of your used one will be much more than that.
By the way: I got an irresistible offer for a MacBook 12 512 GB and I jumped on it - I postponed my purchase to next year, until the battery problems are solved