I have also the experience that D7 is slower than D6, but after some tweaking I think the difference is minimal
- switch off the overlay module (drush dis overlay toolbar)
- You will also need to tune MySQL innodb database engine as that is now the default database for Drupal 7. I found that after I had done #1 and #2, tuning the innodb made a pretty big difference for some dynamic pages. For more see my Tuning Innodb page.
and Drupal is slow because of Server Side Caching and things
- Switch off the Devel modules if you have them installed
- switch off the Update Manager Module (drush dis update)
Now my Drupal seems still a bit slow on admin pages (with several modules installed), but not much slower than D6.
Turn on Keep Alive to allow more than one part of a web page to be downloaded from the server at once. Change the settings in the apache config (/etc/httpd/conf/httpd.conf on CentOS)
As the Views module is the most popular contributed module, most of us are using it to display content is various ways. Views instances should be cached so that when accessed, a cached copy is returned instead of having to rebuild each view every time it's loaded. Most Views should have some sort of caching enabled. If the View generates a block then block caching is the best option.
Drupal6 can be sped up too
compressing the CSS file from Drupal can really help pages. Download the CSS_Gzip module and install it.