any help about flour and rise

Hi everyone, i feel its time i tried getting other peoples opinions on this one.

i have been trying for about 4 months to get a really good rise from the organic flour i have been using.

i have been sticking to the same recipe and changing each variable to see what the cause was..

i have been using jeff hammelmans pain au levain with whole wheat flour recipe.

i have tried 2 organic flours. one grown here in new zealand and another from australia. The new zealand flour is rated 11.9% and the australian 12.5 % protein

i mix and knead by hand using the french method (sometimes referred to as bertinet method?) -  i have tried doing it by feel kneading for 10 -15 minutes, then 2 stretch and folds while bulk proving.

i have tried increasing the stretch and folds, and increasing the amount of stretch, i have tried kneading it for up to 20 minutes or trying to get to 600 repeatitions.

And have tried all of the above with the addition of extra gluten flour and also without the gluten flour.

i have tried short rising periods at 70-75 degrees and i have tried 12 -18 hour rises either retarded in the fridge or on cool bench top (its winter here).

When i look at other bakers results it makes me wonder....because my loaves dont expand like i have seen and experienced before.(i volunteered in a woodfired bakery and got to see touch and feel and shape and bake sourdough that rises to a full volume. so after all my efforts im starting to get frustrated.

the conclusions iv come too are....its either because im not using a mixer or its the flour....

if i use crappy supermarket flour non organic and bleached the bread rises better and holds its shape with strength when i shape it,

i guess the thing im wanting to know is why is my dough so slack. its only a 68% hydration dough, im kneading it to death, iv tried extra gluten. folds, time and temp, steam no steam, extra steam and still the same disappointing loaf.. moderately risen, no real expansion and tearing where iv slashed.

any ideas?

would mixing in a machine help this or is my 600 revolutions by hand enough?

cheers

james