Serial port performance did not scale well on early pcs, so an industry was grown with smart serial cards. There were a few serial cards, but most didn't have the smarts, just shared interrupts. Best performing, in my usage, was the Stallion brand, an Australian company. These cards had their own processor, uarts and ram. Had used 4-32 ports. I am guessing they did high speed transfers via the high speed bus on the PC, relieving the main CPU from getting interrupts, doing queuing, caching etc. These cards were supported by SCO products like Xenix and Unix, some others and ran on a PC.
Flying aircraft could be efficient for some visits that didn't have direct city pairs served by airlines, especially the US. Plus a lot of fun, if you do it yourself.
I used to push statistical and financial data around Australia in the 80s via dial up using automated scripting with Zmodem, Sun hosts, PC remotes. Was very reliable.
IBM NDAs and legals can feel overwhelming in meetings....
Serge