We saved the most interesting benchmark for last: Grand Theft Auto IV.
It's the most interesting for our purposes because GTA IV actually reports the exact amount of graphics card RAM it needs for the graphical settings the user chooses, which is absolutely perfect for our purposes. It turns the theoretical into tangible when you can see the actual memory usage impact of choosing higher draw distances, texture resolution, shadow fidelity, and resolution.
We did have to use a little trick to force GTA into allowing us to use more video memory than what our 512MB and 1GB video cards offered. By making a text file called "commandline.txt" that contains the command "-norestrictions," the game allowed us to choose settings beyond the capabilities of the hardware.
In this case, we first ran settings that would use just under 500MB of memory at 2560x1600. We then ran a second run that used over 1GB of video memory to see what would happen to the 512MB and 1GB cards compared to their 2GB counterpart.
First, we'll try the benchmark using less than 500MB of video RAM:
There are no surprises as there is no difference. Now, we'll see what happens when we use over 1GB of texture RAM:
There's some contrast for you: the 512MB card is completely unable to run the game at this demanding setting. The 1GB card is able to run surprisingly close to the 2GB card up to 1920x1200, but it takes a notable hit at 2560x1600.