Thanks, all! The weather forecast for our mid-June window is currently for rain and snow, so we may opt to postpone anyway. I'm pretty comfortable and competent with ice axe and crampons, but at 56, I'm no longer testosterone poisoned. So I would say: pleasant and safe climbing conditions > frustrating but not death-dealing scree in a couloir > objective hazard of death on steep snow without a safe runout All of which makes me incline toward a later trip.
Someone years ago told me that the best season to climb Stuart via the Cascadian Couloir scramble route is late spring, when there is still enough snow that you can climb the boot track rather than choss. So I've been planning a climb in mid-June with a few scrambling friends. But others have argued that scrambling the top part of the route is a lot easier when it's snow free. Opinions?