Honestly the overhead of a modern OS, especially one like Linux which has been finetuned for these sorts of workloads is negligible. More importantly, any gains

Honestly the overhead of a modern OS, especially one like Linux which has been finetuned for these sorts of workloads is negligible. More importantly, any gains you make by stripping out parts of the OS you don't need you immediately throw away by going for a virtualised, sandboxed ISA. If you want to squeeze more performance per watt than you can get from a modern server, the only way forward is to code your application in Verilog and to run it on an FPGA or ASIC.