*edit: What is FSAA? I am kind of drunk right now and read through your statement a little too quickly to respond.
FSAA is full screen antialiasing...
basically where ever you have lets say a few pixels witch clearly different color patterns or geometry detail, it'll try to smooth these staircase style pixels so that you get a better clearer image... this is most useful at lower resolution where you can most definitely see that uglyness.... many people gaming on a small screen at high resolutions aren't going to notice it... people with a larger screen and smaller resolution will.
Example is some people play at 1080p (1920x1080) on a 20-24 inch monitor.. this is a VERY high pixel density making it usually not entirely necessary to have FSAA.. or to have it at a low value like 2x...
Where as someone playing at 1080p on a 55 inch monitor/tv is going to have a VERY low pixel density compared... resulting in the ailiasing being seen much more clearly.....at which point FSAA settings above 2x would make a significantly larger differences to the picture quality.
The whole idea is simply this
The higher the resolution the less likely you need FSAA or the lower the FSAA will need to be.
The larger the screen at the same resolution, the more FSAA you need to have.
Typically for every additional jump in FSAA will usually require an expontentual amount more vram to provide...... @ 1080p, a 1gb card is typically got room for 2 or 4x fsaa..... anything more and it'll run low on vram.. this is even worse if your using hd textures.
2gb ram at the same resolution will usually make a higher FSAA mode much much easier to handle.
Mutlisampling FSAA is one of the poorest methods of FSAA..... Adaptive is a good idea for high frame rate senarios... but doesn't look much better than a lower mode at low resolution... some games don't like it either..... super sampling cannot be touched... it's the best.. combine that with various type of secondary fsaa modes like narrow tent or edge detect where the later is the most ultimate mode...... will start to sevearly stranging your gpu.
The best mode for the best quality possible with a total disregard for fps. is using Super Samling Edge Detect FSAA .....