Yes, the savings is quite significant. From a hand-selected list of one user's habits, I was able to reduce some pages by more than 20%.

The other thing is that this is not a collection of URLs from across the entire web. The URLs being crawled vary, but the proxy is part of a kind of "portal". So there are potentially thousands of URLs, but they come from a select list of sites. Thus the reason I am looking for the weighting of substrings.

If one URL or one particular site (i.e. a particular substring) is crawled extremely frequently, then imploding that string might be much more bandwidth saving than simply imploding "http://" on all URLs.

mG.