Few settings I'd recommend you to change...
- Use nVidia PCSS vs Sharp Shadows. They give a better, more realistic look to shadows and doesnt kill GPU resource. [comparison]. Notice how the shadow blurs out as the distance gets higher.
- Use 4X MSAA and you should get TXAA option available. TXAA essentially gives MSAA (times two) result without sacrificing GPU power.
In other words:
2X MSAA + TXAA = 4X MSAA
4X MSAA + TXAA = 8X MSAA
8X MSAA + TXAA = 16X MSAA [which doesnt exist - therefore TXAA is greyed out at 8X MSAA]
In Advance Graphics - you can go all the way to the top with Distance and it should'nt affect your GPU [as long as you use the settings above].
I'm using the ultra settings like you except the changes I highlighted above. Granted my system is a little higher specd than yours [i7 & 16GB RAM] but it should only be a difference of 5 fps. My FPS in city is around 60, and 50 on the open roads with grass around. 40 if im surrounded by grass. [ultra grass + high res shadow is a killer >.<]
These settings are also recommended by nVidia Geforce Experience when you ask the software to give the highest quality compared to optimal settings.
EDIT: For those of you interested in nVidia's guide to GTA 5 Graphic settings -
Grand Theft Auto V PC Graphics & Performance Guide | GeForce