IIS 7.5 inconsistently Gzips files (with PHP & ASP.NET)

I found a likely culprit in the comments of this page; weblog.west-wind.com

Essentially, OOTB, IIS will only gzip if the file is requested at least twice in 10 seconds.

This is tuned via in web.config - unfortunately that's locked by default so you have to edit applicationhost.config to change the overrideModeDefault="DENY" to ALLOW.

Reference for that is here: forums.iis.net

Relevant config snippets are as follows. You will see I am also messing with the content type for SVG fonts as by default IIS will not gzip them, so by forcing them to text/xml they get compressed too. (Google PageSpeed complains about this)

web.config

  <system.webServer>
        <serverRuntime frequentHitThreshold="1" enabled="true" />
        <staticContent>
              <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="30.00:00:00" />
              <remove fileExtension=".svg" />
              <mimeMap fileExtension=".svg" mimeType="text/xml" />
        </staticContent>
        <httpCompression directory="%SystemDrive%\inetpub\temp\IIS Temporary Compressed Files">
            <scheme name="gzip" dll="%Windir%\system32\inetsrv\gzip.dll" />
            <dynamicTypes>
                <add mimeType="*/*" enabled="true" />
            </dynamicTypes>
            <staticTypes>
                <add mimeType="image/svg+xml" enabled="true" />
                <add mimeType="text/xml" enabled="true" />
                <add mimeType="*/*" enabled="true" />
            </staticTypes>
        </httpCompression>
        <urlCompression doStaticCompression="true" doDynamicCompression="true"/>
    </system.webServer>

applicationHost.config

      <section name="serverRuntime" overrideModeDefault="Allow" />