Every user of Word 2008, frequent or non-frequent, will be able to confirm that in terms of speed, the application was not impressive. Word 2008 made a big impact on the RAM available on the Mac it ran on. With Word 2011, Microsoft vowed to improve this. These test results, done directly after a reboot with no other apps open illustrate the progress made.
Word 2011, Opening of a Blank document 7 seconds
Word 2008, Opening of a Blank document 9 seconds
Word 2011, Opening of a 40.000 word document 14 seconds
Word 2008, Opening of a 40.000 word document 18 seconds
The above findings clearly show that progress has been made in terms of speed. While there are other factors that determine the speed during usage, such as scrolling speed, speed of saving a document, speed of adding pictures, etc, these tests show that the very first version of Word 2011 is faster than a fully upgraded version of Word 2008. As Microsoft will surely keep updating its latest version of Word, speed will definitely not suffer.