--perf-profile sets keep-alive, flush interval, yamux stream window, and copy buffer; override any of them with the SEIKAN_* vars from the Server reference.

Profile keep-alive flush stream window copy buffer
balanced (default) on immediate 1 MiB 64 KiB
latency on immediate 256 KiB 32 KiB
throughput on batched 8 MiB 256 KiB

Keep-alive reuses tunnel streams across requests (biggest win for many small requests). The larger stream window helps throughput on high bandwidth-delay-product links (a 256 KiB window caps ~26 Mbit/s at 50 ms RTT).