Thanks. Can I really set it to 8192?
You can, but it didn't make any benefit. SE will be RAM-limited, so VRAM usage will not be more than 2-4 Gb. Anyway, SE doesn't need so many memory for now.
Or even 16384 if I include my system RAM? Would that even make a difference?
You can't "include system RAM". Video RAM and system RAM are physically different hardware, and have different purpose. They cannot replace each other.