I guess latency in connection setup isn't really important when transferring high quality pictures, the bandwidth is going to affect the transfer time much more

I guess latency in connection setup isn't really important when transferring high quality pictures, the bandwidth is going to affect the transfer time much more. I see your point about a better connection between S3 and CF, but it's a hypothesis, and the docs don't confirm it. My experience with CF is that the first fetch (for GETs) tends to be "slow"; I don't have enough numbers to check whether is as slow as S3 (whose speed is highly variant over time) or not. But I have always thought that the speed of S3 was impacted by "I/O" (virtual I/O) time, not network or bandwidth. EC2 servers which are in the same region are able to sustain much higher transfer rates.