I used 3/4" copper mains with 1/2" copper drops in my last shop. It worked well for the 25+ years I was in that shop. I started with just a main from the compressor around the workbenches and then added to the system over the years as tools moved around the shop and equipment was added. We have also used copper in all of our shops at work and most have been in service since mid-80's with no issues.
Personally I wouldn't run black pipe after what we have to deal with in our fire suppression systems and moisture as they eventually rot through.
In my new shop I was going to go with copper again but I knew ahead of time where I wanted everything and I wanted a lot more drops than in my previous shop, plus this is 3x the size and when I started putting a pencil to it I found it was adding up quickly. For the cost I just went ahead and went with the Aircom system, which is identical to the RapidAir but I went with the 1" (25mm) aluminum tubing in sticks vs. the rolls. I highly recommend either the RapidAir system or the Aircom system. No having to deal with sweating in fittings and messing with painted walls if you decide to alter something or add something later.
I used 3 kits and this was all that I had remaining.
It is nice to work with. Cut & debur then insert into the compression style unions or "T's". I ended up with 9 drops in the shop, 7 of those with dual manifolds and 2 of those drops are my air hose reels. In the RV bay I have 2 drops as well.
Mike