If you haven’t watched the GDC Open World demo video then make sure to take a look at that since they deal with performance stuff.
For something like the GTX 470 I’d turn off some things, like SSR, which wasn’t in games at the time that graphics card came out. If you haven’t setup batching/static mesh instancing then look into that, though that depends on if the number of objects is one of your issues. Check your stats during gameplay to see what things are taking the most render time.