Internet explorer slow, in private Browsing fast

Hi,

I'm having performance issues with Internet explorer for a number of users. as an example easyjet.com is slow and takes over 10 seconds to load. However if i switch to in private browsing the same site loads in around a second. I have tried disabling all toolbars and extensions and disabling Protected mode. Are there other settings that in private browsing disables?

Thanks,

Nick