What do you need the copper for? 500 is quite a bit, does it *need* to go back to the base? if you are using it for gear, it might be worth it to build a new base/smelter/forge and build the gear you need, and portal that back. It also depends on the distance involved, I've never moved large amounts of copper great distances (All close enough so that making a road to my main base is pretty easy), but I have done with Iron/Silver, and in that event it's almost always best to find a sea route with short hops with a cart, as a full cart, even with a road as climbing inclines can be a real pain.

For me personally, i find i like building infrastructure, so will literally spend a day building all that i need to transport the goods, instead of trying to haul it without it. but That wouldn't count as the quickest..