well, try them all, in all keys, on one string, two, three, skipping one string, two, in triplets, in 8th notes, legato, alternate picking, economy picking, backwards, at 40 bpm, up to 210 bpm, following every mode, the harmonic minor, every mode of the harmonic minor, mixing the rhythms... Now you have another set of exercices.
Check out 'rock discipline' by John PETRUCCI, it's pretty much the same spirit. And if you get bored, try the REH tapes 'power licks' by Shawn LANE...
(by the way, my post is serious, the book rock discipline is a ripoff, it could be only four exercices with what I just wrote under them, except they wrote them all)