I have not tried routers yet, so I am going to go look into that. And the only reason I am not doing export buses is just my attempt to keep space use to a minimum, as I have 3 64x64 quarries running at full speed at any given time. If I wanted to do all the ore at once I would need more furnaces.
Actually, there is no reason not to use export busses. One bus handles up to 8 ore types in the queue, feed multiple busses into the same router hooked up to a wall of furnaces. Even if you backlog, it will just hold the extra ores in your storage until there is free processing room. The only issue you might have is if even over an extended period of time you are bringing in more ore than you can process, but at that point why are you even bringing in that much ore? If you cant even process it with 100% furnace utilization, doing it on demand and going below 100% is just going to make the backlog worse.