I bake two loaves of this sourdough most weekends. Since I've learned to control the temperature during the whole process, I'm getting consistent results every time.
My formula is from Hamelman's Bread - Vermont Sourdough with 10% organic rye flour. My wife likes more sour flavour, so I retard the final fermentation in the refridgerator for about 8 hours. I was worried at first that I wouldn't get the over spring, but I take the dough from the refrigerator and straight into the oven and get the same results. There is a marked increase in the level of sourness.