Okay, erm... I had my theory grade 5 like a few years ago and i haven't touch any theory stuff since... I scored Distinction for grade 5 but i was thinking to pick up grade 6 only when i complete grade 8 practical... Do you think that's okay???

I think doing grade 6 theory BEFORE grade 8 practical would help.
I did grade 8 horn after grade 6 theory, and it helped no end.

ive just ogt distinction for grade 5 theory and im starting grade 6 now. im only grade 5 practical

Do you HAVE to have grade 5 theory to take grades 6,7,8 practical, or can you have, say, grade 6 theory but not grade 5? I've already got my grade 5 theory and taken grade 7 practical exam on piano, but I'm just interested.

You need grade 5,before you can do 6 or above in pratical and theory.