1) How do you actually measure performance? 2) How do you deal with performance and variance in individuals? 3) How do you set an acceptable performance level? 4) How do you make allowances for external disruption that affects performance?
With more than 3 years in management, I have personally found that you cannot really measure development performance much more than hand-waving.
A much more effective approach is to find somewhere that each member of the team can have a stake in something and be engaged. Make someone in charge of teh CI server or the deployment server or Git practice or coding challenges. It is much easier to see how people are performing then.