How to change the HTTP GZIP Compression Level for Dynamic Content in IIS7?
Solution 1:
You need to set it in the compression scheme:
http://www.iis.net/ConfigReference/system.webServer/httpCompression/scheme
for example to set it in gzip using AppCmd:
appcmd.exe set config -section:system.webServer/httpCompression /[name='gzip'].dynamicCompressionLevel:"5" /commit:apphost