I just went back and counted how many cycles I could get in with my method. On slowdown ... painfully slow ... and double clicking, I made 63 cycles in one day (August 11 1300 - I opened up an old save). Note that I both buy and sell in each cycle so the ship is always full (eg one cycle would be: buy skins & sell IG, then sell skins & buy IG), so that's not looking much worse than selling manually. Total mouse clicks = 4x63 ~ 250
Most of my manual arbitrage I did on "very slow" instead of "slowdown"; if I'm feeling bored I'll go back and count to see whether or not I still get 63 cycles on "very slow". If so, I'll edit this space just
...
46.
So doing it on very slow is a bit less efficient, but not greatly - and it takes a couple of minutes instead of, well, many more.
Note that all these numbers are done with a trade office, but in my method its presence shouldn't make any difference.