[ajross]

No, TCP performance goes up for the connection in question. Latencies are lower because the packets arrive earlier. Latency (for all protocols) goes down on the whole though due to the backlog.

Balancing these requirements against each other is a really hard problem. TCP slow start is (well, was, c.f. this article) an early attempt to get an auto-tuning solution. But it isn't the only part of the problem, nor is it an optimial (or even "good") solution to its part of the problem. It's defaults are very badly tuned for modern networks (though they'd be a lot better if everyone was using jumbograms...).