From what I understand of the limited control players have on their own Interface and the graphical options of FFXIV, the only way to "Lighten the Load" on the card, is to lower your graphical settings. Unfortunately, to my knowledge, We don't have an NPC / PC number limiter, for FFxIV, so the best you can hope for, is that by lowering your graphical settings it'll kill the speed at which those PC/NPCs load. It's one of the options that SE needs to add into the configuration tool for 2.0 at least in my opinion.