Most of the time PB solves just depend on the luck of the draw. I'm sub-15 and my PB is 8.584, and it was quite a lucky solve. If you do enough solves, you'll eventually get one that goes just the way you want it to. Also being full CN helps a lot.
Regarding the 6.003, after the 4th F2L slot if you were to do R U2 R' U2 (R' F R F') instead of the normal alg you would've gotten a J perm instead if a Y perm