Introducing location-awareness in overlay networks allows for a higher efficiency of the offered services, e.g., shorter search times or higher throughput. This is especially important for business applications supported by overlays. In this paper, we will illustrate how such an increase in efficiency causes congestion in an otherwie well-dimensioned locality-aware overlay using a Distributed Hash Table (DHT). In particular, we will use a Vertical Handover (VHO) support system using a Pastry substrate as an example. We will describe the occuring congestion problem and identify the underlying reasons. Thus, we describe the basic trade-off between efficiency and load-inequality. Furthermore, we introduce a solution for the specific issue observed, and conduct a performance evaluation identifying the major influence factors and optimization potential for future work.