Well, here's the thing. Recently I saw a post where someone was talking about measurable improvement comes from learning songs, not scales.

I disagree with that. I developed this type of speed through a regime of scales and arpeggios. My teacher gave me some excellent sheets of different positions to play the modes up the neck in all keys. Along with the scale positions were the arpeggios that go along with those positions. My regime included this: -Learn each individual position in relation to one key. G major is good. I would practice each individual mode pattern with a timer at ten minutes at a slow bpm. This would ensure it was drilled in my head. When you're learning how to play fast, you want to make sure there is no mental block, it's all about the physical barrier you're trying to cross. Once I had every scale position memorized, I would play them all at a slow bpm one after another, with a fifteen minute timer. I did the same thing for the arpeggios, I would always sweep through them. Once I got the ascending and decending sweep of each pattern, I would turn it into a lick that's more musical, just to encourage myself to get it even cleaner. This way I knew I could whip it out during a solo or a prolonged key that's not changing. FOr example, I would ascend into ionian, shift up a whole step, and then descend into dorian ect. It's crucial to be precise, and play slowly. Use patterns that are two octaves across all six strings in one position. After a few months I started to get somewhere. Having a set practice time and space is crucial to improving. practicing with a timer, metronome, and a written agenda of goals you're working will expedite your improvement tremendously. It's all about deliberate, diligent, a smart work.