IIS 7.5 Slow serving page while it upload to another file host in a separate thread

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http://serverfault.com – I am using Windows 2008 R2 with IIS 7.5, the webpage loads very slowly around 5-10 second to open. User can upload file on my website, after it finished uploading (file around 300MB), my server will create a new thread and using that thread to upload the file to another server. During this process client faces slowness on the whole website, which means that the whole server is busy because of the uploading process running in w3wp. I can't write a program for uploading the file but instead relying on the w3wp. Anyone know how to optimize the process so that i can upload and also serves the si (HowTos)