At loads each node could carry, the gateway added a few milliseconds. A 2 vCPU node held 12,000 requests per second and added about 5 ms. A 4 vCPU node held 25,000 requests per second and added about 2 ms. An 8 vCPU c9g.2xlarge held more than 52,000 requests per second, still at 100% success.
Throughput scaled with the cores. Doubling from 4 to 8 vCPUs roughly doubled the rate, from about 25,000 to more than 52,000 requests per second.
Failure case: The 8 vCPU box found its ceiling at 53,000 requests per second, where success slipped to 99.97%.