If speed is such an important issue, you really should consider switching across to Firefox or Safari. Both are much more stable than IE8, not to mention quicker and better received on a wider level that Microsoft's offering. I believe Firefox is currently the quickest of the mainstream browsers in terms of page load time.
In terms of optimizing IE8 to run faster, you could remove some of the add-ons that are attached to the toolbar and try running less tabs/windows. These can both contribute to slowing down the browser.