The binary drivers are of similar size. The open sores ones are more compact, but don't access the fancier acceleration functions for games etc. IIRC the nvidia open source are barely functional. I do use them on a work pc for a pretty low-end card, and they seem ok for everyday desktop stuff.
“People Are Killing Puppy Clones That Don't Come Out 'Perfect'”
The proprietary drivers are definitely smaller on Linux (~33mb on disk on my system) but that's largely because the Windows drivers contain a shitload of what are essentially runtime-patches for games. A lot of stuff, particularly shaders, in games is poorly coded and nvidia essentially rewrite them, stick them in the drivers, then replace them in the game when it runs. Everyone wins - the games run better and nvidia cards look good. These take up a *lot* of space.
I haven't installed binary drivers for linux in >10 years, they weren't worth the bother. Although they had better 3d acceleration, 2d for typical desktop stuff was kind of sucky.
“People Are Killing Puppy Clones That Don't Come Out 'Perfect'”