In financial networks, the explosive growth of high-frequency trading (HFT), market data feeds, and real-time clearing platforms has only heightened the demand for ultra-low latency and yet secure data transmission. With 400G Ethernet becoming the core of modern financial infrastructure, a complex technical challenge is to implement robust encryption without deterministically degrading system performance. This article discusses the deployment of MACsec on 400G links by leveraging hardware acceleration, including FPGA, SmartNICs, and ASICs. The study compares software-based MACsec with hardware-accelerated alternatives, conducted through emulation, simulation, and benchmarking in lab environments that mimic real-world financial traffic, using metrics such as latency, jitter, CPU utilization, throughput, and power efficiency. Hardware offloading significantly reduces latency induced by encryption and facilitates secure communication within a microsecond bound while also increasing system scalability—a crucial feature for both compliance-sensitive financial applications in practice. Proposes a comprehensive architecture to integrate both legacy and next-generation data center fabrics. The article offers deployment recommendations (mixed plumes vs. deposited samples), key lifecycle management principles, and a guide to component selection tailored to operational needs. This also highlights new trends, such as post-quantum MACsec hardware and AI-driven encrypted traffic visibility. For financial institutions seeking to strike a balance between security and speed in a world of terabit-scale networking, this research offers valuable insights.