Nowadays, an increasing number of organisations have to make decisions about the change and optimization of their enterprise infocommunication infrastructure. The usual approach of performance (using QoS, SLA) is not user (enterprise) centred and complex enough to help ICT (Information and Communication Technology) experts to support management decisions. The paper proposes a strategic management inspired, user centred and complex method of creating KNPIs (Key Network-Performance Indicators) for the measurement. In the paper, a case study is introduced to illustrate the creation and the use of KNPIs: alternatives are generated for the change, and using KNPIs, the feasibility, capacity, quality and financial aspects - integrating also the business impact and the influence of user experience - of the change of the enterprise infocommunication infrastructure are examined and compared. In the case study, to the analysis and prediction of the necessary enterprise network capacities, network traffic simulation is used. Financial modelling is also applied in comparing the alternatives.