It's run fine on my RX6500
on higit/medium settings, without dsr and else. In additional mode w/ Vulcan and ultra settings of shadows and smoothing - 53-60 in tests.
My build lower/middle cost, 8Gb Ram Radeon R9, 3000 Mhz that working on 2400 - 2600 mhz rate, i didnt set timings on it. I cant find another, exactly as this 8gb expansion. There is only 3200 or 2600 variations.
So if you want to comfort game - it's will be. Comfort and beautiful game on ultra settings - possible, if turn perfomance mode / dsr / tweaks. But i really think - that game is beatiful any way, on any settings and any hardware. That game beautiful by it content
* About your trouble w/ ERR_GFX_INT error.
- Got that once, after few days of playing RDR, when AMD Adrenaline installed new ver. + CLEAR DRIVER INSTALL.
Exactly this error on ONLY RDR2 other games and apps works fine. Roll back to lower ver. of AMD Software, thats show as recomended, or reinstall clearly Software with your basic drivers, that you can download on videocard manufacturer, and update to last recommend ver. of drivers and software.
After - if you got a legal copy, check game on errors(you may delete few files in directory) - it will repair by launcher.
If you are playing another copy of game - than you have to reinstall it fully. And it will work. GLHF