[A_Beer_Clinked]

I did a little searching to expand on your numbers. What follows is not scientific.

According to https://www.datanyze.com/market-share/cdn/ CloudFront, Akamai, MaxCDN, CloudFlare, EdgeCast and CDNEtworks account for ~75% of CDN usage by the Alexa top 1M (with 28 others listed)

Data from http://trends.builtwith.com/javascript/jQuery suggests that the 1.4.2, 1.7.1, 1.7.2, 1.8.3 versions of JQuery are cover 53% of the 23M the have version data for (with 23 others listed)

That puts a lower bound of 690 on the number CDN-Version pairs in the wild.

If we make the (totally unsupported!) assumption that the distribution of versions is the same across all CDNs than 20 of these CDN-Version account for ~25% of the versions.

This could suggest that there is a cache advantage towards using Jquery 1.4.2 (21%) served by Akamai(37.5%)

Seems like jacquesm should now have the data to test this and give us a actual answer.