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no, that is not the problem. oh i admit that ping time jitter is ~random. but even if it weren't, RTT doesn't drive performance, (bw*delay)-loss does.

And how does "delay" differ from RTT, except for the obvious constant factor?

my point wasn't that rtt didn't matter but that bandwidth and loss also matter. so does filesize. for a 2MB GIF i'd rather have a 900ms * 622Mb/s (satellite?) link. for a 2K frame i'd rather have a 60ms * 56K link. using RTT by itself as a performance predictor is just silly. same for aspath length. the only way to know if performance will differ between server/proxy A vs B when talking to client C is to serve from both and see what the tcp window does and what the total bytes/sec are (if the file is long enough for those to matter.) the data then decays rapidly since congestion and routing will change after measurement.