I think lighter is relative here. 3/4" MDF vs Plywood is about the same, IMO when it comes to moving it in any capacity. Even if birch were 10 pounds lighter per sheet, the difference between a 80 and 120 pound object is minimal at that point.
I have sanded pine for a project I did at home. I am at work and don't have access to the pictures, but I would be happy to dig some up to give you an idea of what it will look like pre-stain.