Do any of you know/have FMS Grey Speaker Cables?

I got these over 13 years ago and they are the only thing left I have from my original system and that I'm still using. Does anyone know how they would compare to what is out there now? They have performed faithfully through all the changes but I don't know how good they are and if I'd get a big improvement if I replaced them.

They are grey in color and a an OFC copper stranded litz wire surrounding a teflon core.

Thanks for any info!