Flour Question

I mill locally grown wheat for use in my sourdough breads. The farmer grows a pastry wheat at 8.5% protein (it is a winter wheat if that matters) and she grows a high gluten bread flour, at 14.5-15% protein (a spring wheat) I feel that the high gluten flour, while great for whole wheat breads, makes a too chewy and sometimes dry/tight sort of bread, despite the rather high hydration of the loaves I produce. (I sift it to a 80-82% extraction for formulas that call for bread flour) Yes the oven spring is nice, but I just feel like the flour would be more appropriate for bagels and the like. So, in the past, in warmer months, I did make a few loaves of 50/50 hard and soft wheat, and had great success--but this was in warmer weather. As it started to grow a little cooler, I was producing bad loaves (though with yeast water, not SD, which I haven't yet tried) and switched back to all hard spring wheat.

I was thinking, how much would I have to blend of the two flours to get at about 11% protein, a flour with a med. strength, so I get the breads again with the irregular open crumb and moist texture. (There was a time this past summer I did manage to achieve that with even straight high gluten flour, though it was a little chewier than preferred-- now the crumb is drier and a bit tighter now that it is cooler, maybe the wheat has changed too?)

I was also thinking of lowering hydration with a softer flour to 65-67% and increasing the percentage of levain in my loaves to about 40-50% of the total formula, and also lowering the hydration of the starter to about 65%, in hopes that the acidity will strengthen up the dough a bit.

When I have made breads with a blend of hard/soft, I always found the dough nice to work with, very extensible and still even held its shape quite well, I am wondering if it problems may be in proofing, excessive hydration, or maybe it is a matter of strength...

But I would like to use more softer flours as they do grow much better here in WI, the hard spring wheat does not yield no where close to the soft winter wheat does. I have talked about to the grower about next year planting a winter wheat with a med. strength protein content, I mentioned how the protein in winter wheat is supposed to be of higher quality anyways, read that from Hammelman's Bread. This interested the grower. But for now, the idea of softer flour intersts me and I have been pouring over TFL pages looking at past entries on the subject. But I would like a little more advice if possible--thank you very much!