I have a custom PC I built for XIV that can easily play that game on the highest settings (8,400 Benchmark, max settings)
I can play XI just fine maxed, but you should know there's a graphics card glitch with the game where you can't have weather+shadows on at the same time or it'll randomly go black.
FFXI is a very old game, it hasn't aged well at all.. And after playing on the North American FFXIV servers I'll never play on a JP server again.. the latency is gone, everything is super fast.
XIV was also built on PC and ported to PS3, so the core system will have none of the XI limitations.
People need to stop looking at SE through the Eyes of early XI. They made plenty of mistakes in their first MMO (XI) but I have to get them 110% for learning their lessons in XIV: A Realm Reborn. Yoshi has litereally personally addressed every single issue I can possibly think of. The post he made last week took me about an hour to read, it was literally a novel detailing why, how and what they addressed, in XIV. No company anywhere is doing what they are doing in XIV.