Mouse hover effects can hurt the scrolling performance a lot. That's why Smooth Key Scroll has the option to automatically disable hover effects while you are scrolling, and turn them back on when you stop. Read more about it in this and that articles. This and other options can be customized in the extension's options page.
After having some text selected, you can expand or contract the selection by using the directional keys while having the Shift key ⇧ pressed.
You can press the space key to make small jumps down on the page.
Press the Command key together with the Up and Down arrows (⌘ + ↑/↓) to jump to the end or beginning of the page. (Only works on Mac OS X, otherwise you can use Page Up/Down keys)