New GPU to replace R9 380?

[lazyfortress]

I have an XFX Radeon R9 380.  I've had it since 2015.  Unfortunately, it seems as if most of my games have lagging frame rates.  I was debating between the RX 580 by AMD or the GTX 1060 by Nvidia.  

 

Here's what I would like to see improve:

• Better Assetto Corsa FPS, smoother overall gameplay
• Absolutely minimal FSX FPS lag
• Something that can handle Assetto Corsa Competizione with minimal lag (planning on buying that game soon)

I'm not sure how much of a better experience a RX580/GTX1060 would give me.  How much of a change would I see with these 2 GPUs?

 

I could also save up for about a month and get a GTX1070/GTX1070ti or a Vega 56.

Any suggestions?  Also, are there any performance differences in companies like MSi, ASUS, or Gigabyte if they manufacture the same card?

 

I prefer a 2 fan GPU.  If 3 fans, I could probably cut into my two-thirds empty HDD bay to fit the GPU.  

 

Any information or advice is appreciated!

 

Edit:  I have an Intel i5-8400, and 8GB DDR4 RAM.  I also have a 1TB WD Blue HDD.

[DrMacintosh]

An RX 580 will just over double your GPU performance. You can buy now or wait until AMD releases their RX 590 which is 12nm vs Polaris which is on 14nm rn.