In this paper, a delay sensitive, energy efficient and quality of service (QoS) oriented WSN data gathering protocol has been developed using single mobile sink node. We exploit an enhanced centralized clustering model using expectation-maximization (EEM) concept to enable reliable and energy efficient clustering based data transmission. To reduce energy exhaustion and signaling overheads due to more number of clusters, we derived an optimal cluster count model. To enable time-efficient WSN data gathering the use of inter-node distance (dist(CNs _CH _Mobile Sink)or CNs _Mobile Sink) based dual transmission strategy has exhibited optimal data gathering. The overall results exhibit that the proposed EEM based clustering with optimal cluster selection and optimal dynamic transmission decision enables higher throughput, fast data gathering, minima delay and energy consumption, and higher efficiency.