WebSite Performance decreasing due to heavy page size

Hi,

In my website for one project we have 5000+ records in sql database. If I give page size is 100 for gridview then the paze size showing 800kb in firebug net panel and it is taking 20-30 seconds to load webpage. If I give page size is 10 for gridview then the paze size showing 160kb in firebug net panel and it is taking 5-6 seconds to load webpage.  If I give page size is 5 for gridview then the paze size showing 130kb in firebug net panel and it is taking less than 6 seconds to load webpage. I noticed that due to heavy paze size the performance decreasing but as per my requirent the paze size should be 100 or above and the page should be load less than 2 seconds. Can anyone help me how can i achieve above senario??

Note: I am using Ajax Update panels

Thanks