In view of my recent days of using Slackware 13.1, I am officially tagging this issue as SOLVED. If anyone else still has major problems with Wi-Fi (not just slightly lower performance than Windows), my recommendation is to upgrade your kernel to at least 18.104.22.168 (the one I'm using) or perhaps try the stable or bleeding-edge drivers that can be found at the same source suggested by rsisto, namely:
Thanks to all for your efforts. May we see further improvements such as this in an near future. Jolly day, everyone.