If you are not in hurry and want to develop robust reward calculating and performance system. I suggest please go for SEI institute KRA i.e. Key Result Area.
Basically I developed a detailed specification based on KRA of SEI five levels. But you can use KRA to judge performance of each employee and it would also help you resolve conflicts between them.
Design the KRA or each employee and ask them to fulfill criteria and evaluate on them. Very widely adopted performance management system even by large International MNCs.
You will easily find information on web about it.
14th August 2014 From India, Delhi