Modern data center networks must support a multitude of diverse and demanding workloads at low cost and even the most simple architectural choices can impact mission-critical application performance. This forces network architects to continually evaluate tradeoffs between ideal designs and pragmatic, cost effective solutions. In real commercial environments the number of parameters that the architect can control is fairly limited and typically includes only the choice of topology, link speeds, over subscription, and switch buffer sizes. In this paper we provide some guidance to the network architect about the impact these choices have on data path performance. We analyze Leaf-Spine topologies under realistic traffic workloads via high-fidelity simulations and identify what is important for performance and what is not important.