There are so many settings.
With fxaa, you can run everything on max minus perhaps the grass. I run the grass on ultra but sometimes i dont like the frame rate going in the low 40s. The grass on ultra will be hard to run with MSAA......well, on the outskirts of town. The city is fine
it wont be 60fps everywhere. GTA 5 has very brutal areas. The frame rates depend on your location. I get mostly 50-60s with vsync on. But there are very demanding locations and i dip below 50. Luckily GTA 5 is pretty well optimized and the experience doesnt suffer too much. But i would be lying if i told you that i havent been thinking "i wonder what the titan X would be like"
With an overclocked 980, I can max out everything with 2x msaa + txaa. but the grass is brutal in the country and outskirts of town. With fxaa, it is better but still it isnt where i want it. Grass on very high, that is much better.
You will be able to max out almost everything. Go easy on the MSAA. FXAA is okay. You need some AA in this game, that is for sure. SuperSampling, anything.
Not sure if TXAA will work with AMD hardware, but i do find it to be the best as far as the ingame AA options go