In this paper we consider the deployment of 3D-MIMO in traditional LTE bands (~1.8-3.5GHz) though 3D-MIMO is also considered an integral element of 5G systems. We show how the architecture of the 3D-MIMO antenna system (i.e., the connectivity between the transceivers and the physical antenna elements) can significantly impact system performance. At the cost of additional complexity in the array architecture that affects the ability to form wide or narrow RF beams, substantial performance gains can be achieved. We also consider the effect of the deployment scenario on 3D-MIMO performance. Generally environments where users are spatially separated in the elevation domain are better suited for MU-MIMO and consequently 3D-MIMO can provide better system performance. We observe that denser deployments (small inter-site distance) and user distributions offering a wider range of elevation angles of departures are more attractive for 3D-MIMO deployments. We present system simulation results quantifying the achievable gains by doubling the number of transceivers (or antenna ports) compared to a state-of-the-art LTE 8Tx base-station while operating within the existing LTE specifications.