This seems like an impossibility, to take into account the torque curve, power output, length of time they can use peak ERS, fuel saving over a lap etc to get the engines within 1-2% as was proposed.
How are the FIA planning on enforcing this? Are they going to limit the power output of the best engines? They can't exactly make the lesser engines perform better.
Also how are they going to stop the teams just looking for new engine based performance measures, such as shrinking the cooling right down to give aerodynamic benefits?
Who will enforce this?