Wildcat can definitely be crowded if you don't leave really early in the morning. It's also pretty bumpy. I'll probably give your route a try next time I go out. On Sunday I did the loop I just described in order to break in my new 1-piece leathers.
For whatever reason, coming down wildcat just makes me uncomfortable. Too steep and slow and weird intersections. It was better on the monster than the 851, and this being a monster board I suppose that's appropriate, but it still always made me nervous.
It is very pretty though.
Marsh Creek has too much traffic for me. Too many hyper-commuting east county drivers, I guess.
Also, if you want a tight road, you can go over to Mt Diablo and ride that. It's like $3 (?) but actually really pretty fun. Come in off Diablo and go out Northgate. Very pretty.