Unfortunately I have the 27" iMac, so the resolution is dangerously high at 2560 x 1440.
These are my priorities when I game:
--------------------------------------------------
a1.
Performance
Must be 60 fps and maintain 50 fps
or more in chaotic, frantic, fast paced situations. Graphic quality MUST not compromise gameplay at all.
a2.
Correct Aspect Ratio
16:9 people. Anything else produces a stretched, skewed, compromised image and messes with the player's perception of how the game physics were intended to be. (To explain: When viewing 4:3 on a 16:9, the height of the given 4:3 resolution remains the same while the width is stretched out, nearly double the original. This is why any object which moves left or right on your screen will appear to move faster than intended by the developers. By almost twice as much. This can be very confusing and compromise gameplay.)
a3.
Specific Graphic Settings
In World of Warcraft, for example, settings like Viewing Distance are DEFINITELY gameplay-compromising. For example when an enemy player can see you 500 yards away and starts coming at you, you MUST be able to see him or her from the same distance, NOT when he or she is right in your face and you're left unprepared and clueless.
a4.
Resolution
The screen resolution must be native, or as close to native as possible. For me, that means either 2560x1440 or 1080p if I have to compromise in order to maintain perfect performance and playability. Sure I wont get to stop and look at all the pretty trees in the heat of combat, but then again I save myself the frustration of watching a 7 frame slideshow of being sprayed by an enemy player over the duration of 5 seconds.
a5.
Graphic Settings
If I can pull off all of the above while still maintaining 60 or more fps, this is where I can allow myself the pleasure of ultra-high texture resolutions and beautiful environment detail, terrain blending, water, etc...
b.
Settings I Deliberately Turn Off
If you ask me, some of these settings are completely unnecessary, and on top of that, can actually hinder one's gameplay. Therefore I choose to completely turn off many settings that have the potential to actually reduce fps by 60% or more.
For example, weather settings seem ridiculous to me. I mean sure they can be beautiful and change the mood of gameplay sometimes, but in all honesty, you're playing a game on your computer, not looking at scenery in British Columbia or whatever. Weather, if you ask me, simply bogs down your system and performance, while managing only to distract you from your goals in the process.
Something else I always keep off are things like light-in-your-eye effects. Sure they make things seem more real, but who wants that in a game anyways, right? Albeit, this setting will not bog down your system as much. But in a scenario where you're in the middle of a heated one-on-one face off with this one enemy player who's been targeting you all evening, you don't wanna be stuck thinking "CRAP MY CHARACTER HAS SUN IN HIS EYE! I SHOULD MOVE I CAN'T SEE ANYTHI--" *death*
--------------------------------------------------
Things You Should Be Aware Of
A few of the settings, such as Anti-Aliasing and the likes, are only intended for presenting the game in a lower-than-intended resolution. When you play on native resolution, you can allow yourself to set AA off and not even notice a difference (especially with a high DPI screen) while saving 20-40% fps. This way you can allow yourself to turn on some settings that actually do make a noticeable difference in gaming quality, such as Anisotropic Filtering.
--------------------------------------------------
Basically, to sum everything up...
When you're playing a video game, and you're making sure your settings are optimized, make sure you stick to your priorities.
Don't do anything that'll compromise actual game-playability, ESPECIALLY when dealing with an online game! Make sure to test your fps after each "apply settings --> reset" scenario. Make sure to test for acceptable fps in ideal situations, and in extreme situations. Don't forget that extreme situations are when you will depend on your fps THE MOST. So don't compromise gameplay during those extreme situations, just so you can have a better time looking at pretty flowers as you frolic through the meadows in between actually playing the game.
Before you even test the graphic settings the first time, TURN OFF THINGS THAT YOU DON'T CARE ABOUT! Some gaming geeks buy a 4x SLi setup that cost more than a 2011 Hyundai Accent for the initial high they get from putting all of their settings on ultra high with native resolution on their 68 inch 16,000 x 9,000 resolution, while alt-tabbing to five 1080p movies all being watched at the same time.
Don't try to feel awesome for being able to make your game run at absolute maximum settings. Be realistic and turn off things you don't care about, you can always turn them on later if the FPS allows, once everything else is done. Settings like light-in-your-eye, weather, or shadows, for example. They do nothing for actual game playability.
Also, make sure to turn on things that you
simply don't need!. For example, if you're playing at native resolution on a modern, high DPI iMac, you absolutely will not need Anti Aliasing. Turning it on even at 2x will simply put more strain on your GPU for absolutely no reason whatsoever. You will not see a difference, and you are (albeit shortly, but still) shortening the life of your GPU, while pulling down your fps by a substantial amount.
*edit* I really don't know why I just wrote this whole guide. Nearly everything here is implied to most gamers. I must be really bored. Oh well, now it's here for anyone that may want to read it. I should probably go have a smoke and play some Warcraft
