I bought a used Powercolor Red Devil 5700 for $190. My intention was to play with it, screw around with BIOS, voltages, timings, coolers (including water blocks) etc. I have 2 RTX 2070 Supers, 2 GTX 1080's, a 1080 Ti, an RX 590, several other newer GTX cards. You get the point.
Right now I'm running the RX 5700 (still unchanged after 4+ months) on an LG 4K monitor with a GTX 1070 Super on a 2k right beside it on my other machine. I did have flickering issues on the 5700 at first, turned off FreeSync, fixed. Keep in mind, it's running a 4K monitor, with only OEM BIOS, and no factory OC and there is only a 12 FPS average difference than the 2070 super on Horizon 4, 9 FPS on Shadow of the Tomb Raider and 21 on FarCry 5 (not sure about that one as to why yet). Regardless, you don't visually notice a difference, all specs aside.
And just to try and really piss off fanboys on both sides the RX 5700 is on an i5 9600K build, the RTX 2070 Super is on an R9 3900X.
I will eventually get around to putting the Red Devil 5700 XT BIOS on the card just to see what happens, but the fact remains that when an RX 5700 is working right, even on a 4K monitor, it is more than adequate for the new stuff. Imagine at 1080P what it could do...I don't have a monitor below 2K or I'd have tried it. There were driver issues at the outset, but for all intents have been addressed. Don't fear Radeon, especially with the direction they're headed now. They're about to come out with their newest lines, too, so it might behoove you to wait a little for even better used deals. Nvidia IS still more seamless in drivers, but the difference is so minimal now it's not important.
I've been building for decades. Do it for a living now. If you can find an Nvidia GTX 10 series or an RX 5000 series that meets your budget and performance needs, buy it. Quit looking at paper specs. Don't hesitate to buy used if your purchase is covered (Ebay/PayPal). When's the last time you ever had a GPU or CPU fail after years of use if it's not flashed or OC'd incorrectly, or heated beyond extremes (or had a water leak!)?