I didn't read everything, but HD is also somewhat important when you're trying to load everything. Especially given the fact that all the FPS drops are in the city where the most people are and you have to render them from data saved on your computer.

latency has a minor effect on fps but only because if you have massive packet loss or spiking ping then information isn't hitting your game. So rather than loading everything over the course of 5 seconds you're game's trying to play catch up and load everything at once.

Also one thing that I noticed affects my performance is just all the junk files from cache, leftover registry files after updates. So I run CCleaner and make sure I don't have any malware or spyware since those can take up resources.

But I have 16.7 gb's of ram with a Core i7 980 and the game barely uses any ram, let alone much of my cpu. It uses 70% of my gpu at max load and this is with my graphics on the High (Desktop). I still get crap fps at times, especially when I was doing the Svara fate and everyone spammed their skills. I had to take other people's battle effects and turn them to simplified to solve a lot of my FPS drops there.

But I think all in all, it's the optimization of the game. The point in which people start to load on your screen is my best guess is part of the reason for massive drops in FPS. So until the game becomes better optimized I would suggest tweaking your settings. It's lame, but the game still looks awesome at standard settings.

Oh and on a side note, this may come off as ignorant but I've always used a reputable MOBO such as Asus. I know that Gigabyte and EVGA are also somewhat equal contenders depending on your chipset/options. But I've always heard that ASrock is substandard and so that could be a bottleneck. Technically substandard parts could be limiting the actual potential of everything you have. Your PSU is plenty of enough wattage for a single GPU setup btw. People that say otherwise don't know what they're talking about.