Actually, you may be missing a fundamental part of the equation. 32-bit Operating systems cannot use the full 4 gigs, so you're already handicapped to begin with. Subtract the 128MB of VRAM and without doing precise calcs, off the top of my head I'd say you're right about what you quoted.
So the answer: it's certainly not 4:1. I'm pretty sure it's 1:1, but you don't have full 4 gigs to start with![]()