i've done both summit and la gloria on my r1100rs sporty-touring bike with metzeler z6 touring tires which are about as close to slicks as you can get. easy hard packed wide roads.
summit has been a private maintained road for a lot longer than 20 years. we lived off Casserly near Mt Madonna Rd (behind the county fairgrounds) in the early 80s, and it was that way then.
Experience is what you get when you don't get what you want.