I can use PHP's gzencode function to set the compression level of data to compress and I want to compress my sitemap files then submit them to google.
Currently my compression level is set to 2 because I believe that's a standard value. The highest level is 9. My question is, will (at least all major) search engines support decoding sitemap files that are gzipped at a higher compression level than 2, if so, what's the highest level?
I don't want to use compression level 9 only to find out a search engine could not process the sitemap.