That's a pretty ambitious ride you're talking about.
It's 40 miles, 2700 feet of climbing to start in St Helena, go over Sage Canyon, return on Ink Grade.
From the bottom of Mount George to the top of Howell Mt is 42 miles, 3200 feet of climbing. Of course in the mileage is there some back and forth across the valley, since I pulled it from my Knoxville Double data. But you'd definitely have all that climbing.
I would guess you're looking at a century plus with probably 7,000 feet of climbing.
V.