"So without further ado, we present a selection of comparisons of the game's opening scenes, captured at medium, high and ultra texture settings with all other settings ramped up as high as they go. Monolith recommends a 6GB GPU for the highest possible quality level - and we found that at both 1080p and 2560x1440 resolutions, the game's art ate up between 5.4 to 5.6GB of onboard GDDR5. Meanwhile, the high setting utilises 2.8GB to 3GB"
--Eurogamer
So you see the HD texture pack requires a > 5GB of GDDR5 to provide smooth FPS. I played without it, with default ultra settings, had 70-90 FPS at 1080P. It doesn't matter if you have 4GB of VRAM in ur card for ultra HD.
For Far Cry 4, > 4GB of VRAM in 1080P is pure bulls$it.
Because this
*i1334.photobucket.com/albums/w643/sam_738844/proof_zpsspjop18a.jpg
This is my GTX 970 running FC4 at 2560*1440P @SMAA with Nvidia Soft Shadows, HBAO+ and Enhanced God Rays. There is no way a GTX 970 can face stuttering in 1080P ! in ultra settings.
And if you really want to know about the VRAM issue. Know this.
NVIDIA GTX 970 has on board 4GB of VRAM, yes, read it again, 3.5 GB of vram with max access speed and 0.5GB of less, maxwell memory architecture allows cards like GTX 970 have more than 3GB ( unlike GTX 780 ) with this segmentation. If anyone is asking for a refund because it has less VRAM and ROP's then they should not buy any card in future.
No body discovered this on the next day of purchase by looking at the ROP counts the card has , counts of ROP's or L2 Caches are not mentioned on the box either. It became important when some synthetics did not get enough juice and then referring to Nvidia Marketed specs in internet. Nvidia mislead people on internet, and they are having a lawsuit for that, but FUD over the internet because of performance issue on GTX 970 is akin to steaming pile of shite.