That's coming along very very nicely Ulco.
I think I'd render it with AA8, as you do, but with default sampling at 1/4th.
You can increase renderdetail a bit further, but honestly I do not see much small scale terrain detail which would justify to increase detail beyond 0.6.
Given the resolution and the fact you'll print it this should all be sufficient.
For extra realism you should enable soft-shadows.
I'd re-render this crop with default soft shadows setting and see how fast it renders.
Then render it again and set sample jitter for soft shadows to 0 and see how fast that goes.
Without the sample jitter you may get banding, but that's often difficult to see when the shadow's being cast on bumpy surfaces.
For darker shadows you may need to reduce the GI strength on surface in the enviro light, but you can also reduce the haze/bluesky density since that also affects brightness of shadows.