I think it would be a good idea to focus on either the north or south, rather than zip through the entire state in 8 days. If you're up north, you can choose between San Francisco, Lake Tahoe, Yosemite, Mendocino, and on and on. Plenty for 8 days. You could even head further north to Mount Lassen Volcanic National Park. Really depends what interests you, so you need to provide more info.