About 6x8", across the spread of a Stillman & Birn Epsilon hardbound book
Caran d'Ache Supracolor Soft Ivory Black
I really love working with these Supracolor Soft pencils for studies like this. I haven't pulled any of them out for quite some time, and I forgot how much fun they are! The S&B Epsilon surface is such a friendly support for pencil work. A wet brush with these pencils unifies the darks, and they wash beautifully. They don't erase well, but for preliminary work, I don't mind some stray lines here and there. For a more finished piece, I'd have made my initial marks in graphite, then switched over to the Supracolor when my lines were secure.
If you're concerned about lightfastness when using colored pencils/watercolor pencils (as I am), you can check out this PDF brochure, which contains lightfastness information for the individual pencils, and select ones from open stock with excellent ratings (***).