Skype and Abiword or similar

[Capricorny]

Since you mention LibreOffice, I assume you are running 6.4.4 - otherwise install that.
I have used Skype on Knoppix 6.2.1 - it worked, but not perfectly, on a 3 year old computer. So, it can be done, but old hardware may be too slow/limited. You might try to reinstall/upgrade LibreOffice to make it run faster, it shouldn't be that much of a resource hog. What does top tell you about the state of the system during the too-slow-conditions?

I assume that you have stuffed as much memory as possible into the machine(s). Upgrading from 512 to 2048M on a 5 year old Asus A3hf made a difference for me.

Oh, and I forgot three things:
1. You aren't on a USB1 port? Think some old computers may have a mix of USB1 and 2 drives, like many nowadays have a mix of USB2 and 3.
2. Tried a faster pendrive? You can get them beyond 20MB/s with USB2 - that's not far from some internal 5400 rpm disks.
3. Tried to copy KNOPPIX to hard disk and run from there? Can make everything simpler and speedier - yue can still boot from the pendrive, but you run from HD copy of Knoppix.