Hypax

RAGE Devs = Lamborghini
ScriptHook V Devs = Prius 

Atleast this are their development speeds showed with cars! :D

Pretty much any siren from FedSig or Whelen.  My personal favorite is the FedSig Touchmaster Delta, and is the one I use in-game.  I have a Whelen Gamma2 IRL.

Can anyone help me locate this Tahoe on the site? Non-els!

Hi everyone,
The last day or so I haven't been playing the game's story line as most of you are (I've already played through it a few times on the old versions), instead I've devoted my time to observing the game's graphic options and characteristics. In general, seeing what I can do to squeeze the best graphics out of it with the best FPS possible. After doing countless reboots and benchmark testing, I've found a few helpful things. 
Not all of us are able to afford expensive computers, but that doesn't mean you can't enable higher quality graphics.
As of now, I am able to run the game on Ultra (1080 resolution) with 40 fps average, sometimes higher. Though on the advanced graphics menu, I have all enabled except the extended distance/shadow sliders all the way down.
My hardware:
Intel Core i7 960 @ 3.2 Ghz
 EVGA GTX 680 Superclocked (2 GB)
 12 GB of RAM.
I consider my rig at least mid grade or entry level high end.
All in all, I've found several ways to increase performance:
Run in Borderless Window mode. This allows you to turn off VSync, and you also won't have any screen tearing. Easy FPS boost. On the Population Variety Slider, feel free to move it down. This is a very VRAM hungry option. I believe it has to do with the amount of extras on Peds, such as backpacks or items in general, or the variety of vehicles on the street. If I'm wrong please correct me. I moved it down and noticed little to no difference. Use your sacred VRAM on something more useful! Additionally, if anyone is experiencing random performance drops (such as the game locking up, super low 1-5 fps out of the norm) this is likely caused because of overloading. Decrease this to ease your VRAM. I personally suffered from this and decreased the slider to the near bottom (2 notches) and no longer experienced this.  NVIDIA cards - Use FXAA instead of MSAA. While it may not look as good, it has nearly no performance cost and I can't really see any difference. Additionally, enable it through your control panel rather than in-game for more FXAA options (different levels mostly), while in game you only have one option, which I assume is 16x. AMD cards should also use their equivalent if they want to increase performance. 
NVIDIA cards - Go to the NVIDIA control panel. Enable Threaded Optimization, set Maximum pre-rendered frames to 3, and under power management mode, select Prefer maximum performance.  Additional note: You may select "Ignore Suggested Limits" to On in the in-game graphic settings menu. This allows you to exceed your VRAM limit. I'm personally around 800 MB over my limit and suffer no issues in regards to performance. For those of you who want the most out of this game graphically, I suggest you do the same.  If you prefer to have VSync for any reason, don't enable it in game. Instead, do it through you graphic card's control panel. Along with this, enable Triple Buffering. This helps increase performance while VSync is enabled.  Overclocking:
Note: Overclock at your own risk. I am NOT responsible for any damage caused to your card. You have been warned! 
Download the program for your respective card. For us NVIDIA users, I recommend EVGA Precision X. 
I was able to increase GPU CLOCK OFFSET by 42 MHz, and MEM CLOCK OFFSET by 115 MHz. I have not gone any higher, nor do I plan to as I found the sweet spot for my card. Pushing your card too far may cause overheating, instability, game crashes, and possible damage. You may also increase the fan curve and voltage. Don't mess with voltage unless you know what you're doing. 

I hope this helps many of you and you can enjoy this amazing game to its highest potential. Also, a special thanks to Murphy and Sniper296 for aiding my research. 
If you have any questions or comments, please feel free to reply,
Nick