I am saving obj but it takes forever to save 5gb of hi-res mesh and then even twice of that for loading it into any 3d program or specialised texture baker for baking depth and other textures for a final model.
So what format is the best for that ? Obj is an ancient thing. Perhaps another one from the list would do it better?
Hi kir238
with ANY file format you get in issues as its a BIG model. best if you use SIMPLIFY tool and use around 15-17 Mil tris as a target, with this triangel count you should be able work with almost every 3D sw. Don´t worry the details are “preserved”. Compare full res model with SIMPLIFIED it should be almost the same.
I’d like to know that too!
Why don’t you just try it out and report back here? 
Looks like fbx is a little bit smaller and quicker but also less reliable when loading it into other soft.
As of simplifier I have a problem. I have no idea what the actual size of hi res mesh. Does the program show it somewhere? Thus I can’t estimate properly the target simplified polycount.
From my Zbrush experience I know that decimation works good on some human made objects with a lot of plain surfaces. But on nurture things which are often very noisy by itself a strong decimation is still a loss of tiny subtle details , small cracks. etc.
In a word important details for height/normal textures.
rc_tricount.jpg
Found it, thanks ShadowTail