Due to the way slow-start works the throughput of a TCP connection increases with use (assuming no packet loss) as the congestion window grows. The HTTP test h

Due to the way slow-start works the throughput of a TCP connection increases with use (assuming no packet loss) as the congestion window grows. The HTTP test has images that are ~5KB so after the first round trip for an image the congestion window grows but none of the subsequent requests grow it further, where as in a real world example many of the files would be larger than 5KB the window would grow further an the number of round trips would be reduced. The SPDY example can make use of the ever growing congestion window because the multiplexing will fill it i.e. we'll get the data from more than one image in a single round trip. It's not that the test isn't 'technically real-world' it's that it has (I don't think intentionally) a design that highlights an area where HTTP performs really poorly due to the latency penalty i.e. many very small requests. A more real world test case would mirror a typical page construction with varying file sizes - HTTP Archive can give you some clues here. Have a watch of John Rauser's "TCP and the lower bound of web performance" for more detail on slow start - https://www.youtube.com/watch?v=G6ah2cq4LFY https://www.youtube.com/watch?v=G6ah2cq4LFY