I find being able to speed a passage up past it's actual tempo very valuable for getting something under my fingers. Does anyone know how to modify Riff Repeater so that it the speed setting  can go past 100% ? Would this be easy to do or basically impossible?

Drugs.

I saw that scroll speed can have a .9 value which makes fretboard faster at you, but not a music speedup, something similar to GH fretboard speed, notes just come at you at crazy speed(physically we just set smaller window for rendering notes, similar to zoom at audacity) I think I'll fix bug in Toolkit to allow set things up to .5 (50% speedup of fretboard)

And talking about speed things up, if you do so, game will pitch things up(or no using rubberband, like slow-mo in EOF)
as option use ©DLC2Tab exporter, load tab in GP and set tempo in old fissioned way, practice, ???, profit.