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In brief, the paper's says that under certain assumptions the globally optimal latency would be only 25% better than the selfish result.

If I might, his model says the best is between 0% and a max of 25% better than the selfish result. Selfish routing may actually get us the best possible Internet, although that is not proven.

This sounds a lot like the 80-20 rule. Selfish routing gets you 80%. Infinite knowledge will bring you up to 100% of what is possible but that presumably costs a very large amount of money. --Michael Dillon