Methods, apparatus, and software for optimizing network data flows within constrained systems. The methods enable data to be transferred between PCIe cards in multi-socket server platforms, each platform including a local socket having an InfiniBand (IB) HCA and a remote socket. Data to be transmitted outbound from a platform is transferred from a PCIe card to the platform's IB HCA via a proxied datapath. Data received at a platform may employ a direct PCIe peer-to-peer (P2P) transfer if the destined PCIe card is installed in the local socket or via a proxied datapath if the destined PCIe card is installed in a remote socket. Outbound transfers from a PCIe card in a local socket to the platform's IB HCA may selectively be transferred using an either a proxied data path for larger data transfers or a direct P2P datapath for smaller data transfers. The software is configured to support each of local-local, remote-local, local-remote, and remote-remote data transfers in a manner that is transparent to the software applications generating and receiving the data.