Yes, configuring memory to be used for zram would mark it as unavailable for kernel fs caching.

Does iostat show your disks being pegged when it’s slow? Odd that performance would be so bad on those specs, makes me think you have disk Io issues maybe.

Slackware on a whole lot of lettered floppy disks.

So? Does it need more? Seems to be doing just fine.

Not sure why people think the linux foundation should only do the kernel, it supports a wide variety of open source projects.