I have fast fingers, so semiquaver passages and arpeggios are usually easy as hell for me.
Octaves, however, are another story.
They are my weakness, and I don't know why.
It has nothing to do with strength, because I used to work out a lot, but maybe lack of wrist action? Anyway, the Liszt technical excersizes are quickly fixing that.
Anyhew, screw 3rds, 6ths, 7ths lol. I hate them.