As you mentioned, it's possible to slow down the tempo & that is a great idea until you find the tempo you are able to maintain.  Gradually speed up as you are able.  It is tricky because at a certain point you have to minimize your motion in order to go faster.  And playing at a slower tempo gives you the luxury of wider motions.  So you have to really work at minimizing.  Another thing that is hard to overcome is tension.  That's why practicing at a slower tempo helps reinforce staying loose & relaxed.  So when you increase the tempo you are already trained to stay relaxed.

I do use my pinky, but only in the lower frets when doing the lick down a complete octave.  I can use my pinky, but I find it more efficient to use index, middle, ring in the upper frets for 2 related reasons.  

First, the frets are smaller & closer.  Second, quite often this style of playing requires bending, because this is essentially electric rock style playing.  So, having my ring finger on the top fret of any given position leaves me ready to do that kind of thing.

But as I move to the lower, wider frets I start to use my pinky on the highest note of a position because that is more efficient.  Unless I know I want to include a bend, then I switch to my ring finger which is more stable.

If you want to use your pinky on the higher frets, that's perfectly fine!

Hope that helps!