Is a 4GB graphics card better than 2GBs in 2010 Mac Pro?

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Is a 4GB graphics card better than 2GBs in 2010 Mac Pro

Hi!

I am about to upgrade my graphics card from the stock 5770 in the 2010 Mac pro with a much faster card.

I have the option of a 2gb or a 4gb version.

I use my system for Motion Graphics and VFX Compositing and hear the 4gb is better for 4K projects. BUT I also hear that my systems 2.8 Quad Processor system will bottle neck around 2GB anyway so I won't see that value?

Any opinions on the matter are greatly appreciated!