High percentage starter loaf

hello all

ive been making an organic loaf lately of the following %'s

90% unbleached organic flour

10% wholemeal organic flour

2% salt

1% fresh yeast

50% starter

65% hydration

mix on low for 3-4 minutes,autolyse for 30 minutes, continue mixing until the dough passes the 'windowpane' test. Bulk fermentation for 2 hours with 4 s+f. Shape in to boules and final rise for 1 hour and 30 minutes. Slash and bake at 200c for 30 minutes. 

The resulting loaf has been great, but I want to do a version with 70-75% starter. Would this require any fresh yeast at all (0.5%?) or should I omit fresh yeast completely and allow for a longer bulk fermentation? 

Thanks!