This is in my own private shop, no employees. I have two designated areas, one is more for metalworking the other is for automotive and general things.
I'm in kind of the same boat. Here's my solution:
Double bay "depth" box for complex auto repairs. This box is kitted out with automotive specialty items and is 99% metric.
Roll cart- 80% soution for cars on the apron, diagnostics, light bulb changes. Can do an oil change with this box, maybe an engine accessory. Its a true service cart.
Kennedy roll cab- this is the box in my metal shop. It contains SAE tools, and more pliers and screwdrivers than the other boxes combined. Only metric stuff are allen keys/sockets.
Efficiency experts all tell us to make use of carts and move our tools close to the job. One step away is best. They also say to try to elimiinate twisting. So, having your box on the back wall of the garage and having to turn 180 degrees to access it is not preferred. Better to have it to one side while doing engine work (or work from a cart).
As we get older, I think this stuff becomes more important.
Don't know if you see it, but one of my favorite TV shows in the British car restoration show "Wheeler Dealers". The mechanic on the show (Edd China) has like 4 narrow stacks all around his lift. I'm not sure I understand why. Could it be that one is metric one is SAE? Or is one welding stuff, one electrical?
I get where you are coming from. Might make sense to split your tools up.