No worries,help is always appreciated!
Ok,so here's what I think of this subject.
You say per example "I can play 6 notes per beat at 140bmp".
What does it tell us?
Not too much I'm afraid.
Because there are some licks made of 16th at 100bpm
and they are much harder to play comparing with some
licks made of 16th triplets at 140bpm.
Some licks just feel more natural to play
while some others,even slower,are much much harder.
Odd fingering,uncomfortable picking pattern or whatever.
And this conclusion leads us to only one solution,
practice as much different things as possible,
specially picking stuff cause you pointed on picking.
BPM is only a tool to explain which tempo you are using,
but what are you playing at that tempo is much more important imho.