By staying noodling about in the pentatonic and using it as a scale, you are going to find it difficult to get a good aggressive metal sound. Most of the metal player I listen to, will use their primary scale (lets say the pentatonic), in conjunction with the diatonic (7 note major/minor/modes) scale. They'll also incorporate arpeggio and lick patterns based on both, and usually use the same rhythmic pattern, but switch the scale that they are doing it in. A good example of players, particularly pentatonic based players, who use this are Kirk Hammett, and Zakk Wylde, who has incorporated a lot of Randy Rhodes signature licks and patterns into his playing. (For a great example of this, listen to the end mini solo off Ozzy Osbournes "Bark at the Moon").
Blues music will tend to be very linear, and uses lines through pentatonic and blues scales. This is most likely developed because a blues guitar tries to imitate a singer, who will generally use a tightly grouped set of notes. Metal music licks tend to use wider intervals between the notes in a lot of licks, lending itself to techniques such as 3 note per string pentatonics, and sweep arpeggios.
I'd also agree with Kris and RIP that the tritone is a great interval to use, but it is also the "blue note" in blues music, so you may find yourself back to where you started. So I'd also advise using small patterns, of 3 or 4 notes, that repeat, and you can learn to play super fast, throughout the scale. Then try to work out some arpeggios that use the same type of rhythm as your 3 or 4 note patterns, and learn to move between them.
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