That depends on your performance issues and how far you wish to go to solve them. The 2-hour consult is perfect for fixing a few issues that you are struggling with. In the 8 hour consult I will be able to take a broader look and fix many pagespeed issues. If you are serious about PageSpeed and having a fast site now and in the future you should consider adding me to your team for the next 1 or 2 sprints.