The kind of Graphics Card/Amound of memory on a graphics Card will not make any diffrence to system preformance while running TG 2, The point is The Renderer Uses Normal RAM to store data while it works and CPU to render the graphics. Now your system will run according to the CPU Usage, and since TG 2 uses a large amount of CPU, so if you want a more smooth preformacne with your system while running TG 2, I suggest upgrading your RAM and CPU.
One other Quick Note: Graphics Card upgrades should only be used if you either 1: Play games on your computer or 2: use your computer for other graphic intense programs, such as 3D Modeling programs