IIS - Changing frequentHitThreshold and TimePeriod for gzip for Improved Web Performance

serverRuntime attribute	Description
frequentHitThreshold	Number of times a URL must be requested within the time span specified in thefrequentHitTimePeriod attribute to be considered frequently hit. Must be between 1 and 2147483647. Default is 2.
frequentHitTimePeriod	Time interval in which a URL must be requested the number of times specified in the frequentHitThreshold attribute before it is considered to be frequently hit. Default is 10 seconds.

Add the followgin Web.config
 <system.webServer>
    <serverRuntime frequentHitThreshold="1" frequentHitTimePeriod="10:00:00" />



Unlock command in cmd (otherwise it won't work acess errors):

 C:\Windows\System32\inetsrv>appcmd.exe unlock config /section:system.webServer/s  
 erverRuntime  
 Unlocked section "system.webServer/serverRuntime" at configuration path "MACHINE  
 /WEBROOT/APPHOST".  

If this doesn't work try this:

%windir%\system32\inetsrv\appcmd unlock config -section:system.webServer/serverRuntime

Good Optimisation article:

http://www.codeproject.com/Articles/242133/Making-the-most-out-of-IIS-compression-Part-conf