This is definitely the most challenging part of the song. When I hear it I think it has a big Symphony X vibe.
You'll be using a lot of legato here, including both hammer-ons and pull-offs. It might be tempting to cheat a little bit and get lazy with the legato, but don't!! Make sure the legato notes are as individually distinctive as possible. Even though legato notes blend together, each note should be crystal clear.
There is some pretty fast position-shifting in this riff. I'd recommend completely memorizing it before worrying about any speed whatsoever. That way, once you start building speed, you can always be "looking ahead" throughout the riff and your movements between positions will be smoother.