I've only ever used Knoppix for a recovery CD. As in, when my system breaks for some bizarre reason. Fast you say ? I found Arch Linux is slim and fast. It will depend on your system specs, however Arch with XFCE, is going to be much faster than Fedora and that horrible Gnome shell.
"A HD installed Knoppix will give you a running GNU/Linux system but it is not easy to support or administrate and add/remove of software is complicated and is best left to GNU/Linux experts"
Maybe you should try Linux Mint if your new
or if you want to try to install Arch, Linux questions is here to help. Wouldn't worry though, the documentation for Arch Linux is 1st class, it walks you through step by step.
Edit: Oops yancek beat me to it !