I also use a RX 580 but I get around 25 fps on lowest possible settings , I also get a lot of freezes and stuttering
I’m temporarily using an RX 580 while waiting for RTX 3000.
At 1440p (2560x1440) it manages Ultra @ 19-25 fps in GA aircraft, with few frame dips, but is pretty much unplayable (12-18 fps with stutters) in airliners.
Medium settings works quite well though!
What’s a rtx 3000?
Upcoming GPUs from Nvidia
Ah yes! 
I have the same board. It’s working at 100% of its resources on medium settings. Please see if you can capture what percent your board is working when in GA aircraft with Ultra. That is amazing performance from this board! Also, what cpu do you have to complement this?
GPU is at 100%.
CPU is a 3700X (on PBO) so that probably has something to do with it
Yeah, I believe it does. I just have the Ryzen 5 2600 so…
Which exact card do you have?
I’m using the RX580 Gaming X
sapphire rx580 8GB
I have an RX 580 4GB which has been through it’s paces in a mining rig. With some mild overclocking and paired with a 3700x and 32gb ram, I can get ~20fps on the ground in a busy airport at 1440p high-end settings (with a few modifications). GPU sits at 100% all throughout. Have a 4k monitor - biggest improvement for me was to make sure that I had Windows screen resolution at 1440p, and not have MSFS do the upscaling.
RX580 4gb with mild overclock.
I have an 8gb so that’s probably part of it
The 4k will kill fps compared to 1080p. So much more demanding.
Wow, I didn’t think a 3600 would be that much stronger than a 2600. I have only 4g GPU memory. Bet you have 8g GPU memory.
I have a RX 580 with 4G and 2 monitors connected to it. Will I have any gain connecting the second monitor, witch I use only for flight charts during the game, on the onboard motherboard video connector?
Interesting that you mention those stutters only happen on certain boot-ups. For me, only since recently I also get those very annoying stutters which are clearly due to the GPU. Somehow my RX 580 seems to cease working for 1-2 seconds, which of course causes stutters (nice to see on the screenshot). Happens only on “high speeds of the plane” as if it cannot process all information accordingly…
Sapphire Nitro+ RX580 8Gb Ryzen 5 2600x 16Gb 3200mhz on a 1Tb SSD.
A bit choppy on my 4k monitor but fine on my other monitor native 1080p.
Personal Comments
I spent most of my time from August 2020 launch to last month with an RX 580 8GB. I recently moved to a 12GB 2060.
It shines if you don’t push LOD past 125, and you’re at 1080 with 100 percent scaling. I’m talking low 30s at the most to an easy high 50s at cruise altitude. Of course, you have to be judicious about the extra graphics settings you’re enabling.
It’s a very good card even though it’s old by Internet time and PC Evolution cycles.