This guide works for BOTH LOW END AND HIGH END USERS
I've seen this benefit people with i5-4440 and gtx 750ti with the game on a Hard drive, as well as myself with Ryzen 5 3600X and RTX 2060, and having the game installed on an SSD.
I went from 35-40 fps on default settings to 89-128
I run an average of around 100
and if I am on the mountains, I run 138 or so average, and even reach 144 at times.

This has all been tested at 1080p.
This guide has shown significant increase in FPS on the following rigs:
1)
Ryzen 5 3600X and RTX 2060
16GB DDR4 3200mhz CL16
On SSD

2)
i5-9600K and GTX 1060
16GB DDR4 3200mhz CL16
On HDD

3)
i7-4790 and GTX 745
12GB DDR3 1600mhz CL9
On HDD

4)
i5-4440 and GTX 750ti
16GB DDR3 930mhz CL10
On HDD

This knowledge has been compiled from multiple guides, and personal testing.
The guides in question are:
https://steamproxy.net/sharedfiles/filedetails/?id=416448225
and
https://steamproxy.net/sharedfiles/filedetails/?id=1731305438

I would like to thank both guide makers for helping the ARMA community immensly and I would appreciate if you rate their guides up.

I would also like to thank Spagistan for being such a great, beginner friendly community, who helped me get into ARMA 2 years back. You may find them at https://discord.gg/Hpm52Fw .

Go to your steam library and right click Arma 3, then select properties.
Choose the betas tab, and put this code in: CautionSpecialProfilingAndTestingBranchArma3
Then press check code, and select profiling from the dropdown. You can verify this is done if Arma updates, is called Arma 3 [profiling] and the launcher has a PROFILING sash

The first thing you need to do is figure out whether you are using the default profile in arma, or a second one you made
This can be done by launching the game and looking at the profile screen in the top right
the default profile is always the one you can't delete
(for me it's along)
If you are using the default profile go here
Otherwise go here and to the folder with your profile's name
once you are there, edit the file with just your profile name (no vars) and change these lines to the values shown:
revMouse=0;
mouseSmoothing=0;
mouseAcceleration=0;
fovTop=0.75;
fovLeft=1.3333334;
This will increase your fov, and disable mouse smoothing which can help with accuracy, claustrophobia, motion sickness, and tactical awareness, as well as ease of use.

First you want to figure out if your pc is 64 bit/32 bit, how many cores your CPU has, and if it has Hyperthreading (or a threadcount that doesn't match the core count). You can do this by right clicking This PC in file explorer, and selecting propertiesGoogle your processor's name, and look at it's core and thread count
I will provide two examples Open your launcher and go to the options in the top right, then choose launcher options. In there, you are going to set Action after game start to Close Launcher after clicking Play.
Next you are going to go to PARAMETERS, and go to all ALL PARAMETERS, then make sure your platform is set to 64-bit, skip logos at startup is on, tick on profile and set the one you are using.
Scroll down to advanced, and if your Core and thread count is the same, like the i5-4440, tick on CPU count and set it to your core count.
If your core and thread count do not match (hyper-threading), turn on Enable Hyper-Threading (THIS WORKS ON BOTH INTEL AND AMD), and make sure CPU count is off
if your processor has 6 or more cores or threads (such as processors with 4c/8t, or 6c/12t), tick on Extra Threads and select all three options
Tick on Memory allocator (64-bit) and set it to Intel TBB 4 allocator REGARDLESS OF WHAT CPU YOU HAVE
Tick on Enabled Large-page Support
Make sure System memory limit (64-bit) is off
Find out how much VRAM your GPU has.
Tick on Video Memory limit
if your GPU has 2GB or less, tick off video memory limit
If your GPU has 4 or 5gb, set it to your full amount (1024* amount of GB)
if your GPU has 6gb, set it to 5gb or 5120, and for higher end gpus I reccomend setting it to a bit less than your actual vram amount (I use 8gb on an RTX 3080), just in case.Scroll down all the way and tick on No Pause (in the Author section)

Launch your game and go to video settings
If your GPU has 4GB VRAM or more, Set Texture to Very High (Ultra can have a small detriment on FPS, but not necessarily, test it yourself!), Objects to High, and Terrain to High
If your GPU has 3GB or less, Set texture to Standard, Objects to Low, and Terrain to Low
ALL GPUS: Set Shadow to Standard/High (One or the other will work better depending on your CPU and GPU, but they work the same for me), and particles, cloud, and PIP to Low.
Setting HDR to low may improve framerate, but the game can look significantly worse in many cases.
Set Dynamic Lights to Ultra, and Water Reflections to Standard.
As for view distance,
Overall (CPU/HDD/GPU): Use something like 1050 as Low, 1600 as Standard, 2150 as High, 2700 as Very High and 3800 as Ultra.
Object (CPU/HDD/GPU): Use something like 858 as Low, 1105 as Standard, 1353 as High, 1601 as Very High and 2097 as Ultra.
Shadow (GPU): Leave as 100 or off.
I use Very High for all
Someone with a GTX 750ti or R7 260x level card should use Standard or High
Next, go to Display, and set VSYNC to off. If you experience screen tearing due to it, I'll release a very very short (one or two line edit) guide for VSYNC ON usage later, though be aware, performance is lost this way, and lag is introduced.
Over to AA & PP
Set Bloom, Radial Blur, and Rotation Blur to 0. If you are playing at your monitor's native resolution, set depth of field to 25, and sharpen filter to 10. You can experiment with other values, but I find this the best for native 1080p.
Set AO to HDAO Low
Set Caustics to Disabled
Set FSAA to Disabled
set ATOC to Disabled
set PPAA to SMAA Standard (or SMAA Ultra if you have a lot of Jaggies, but I find a 3-5 fps difference between them)
Set Aniso. Filtering to Ultra
OPTIONAL: I personally like to increase my saturation to 110, but this is a personal preference thing.