Hi,
So I'm not going to waste time mattering like an old lady over tea.
You want 1440P at 60HZ.
Easy enough,
3600x or 2600 it doesn't really change my advice a ton.
Heres my recommendations from doing multiple builds with each these cards.
1. DON'T GET A 2080. ESPECIALLY NOT USED.
Used for 500$ sounds... sketchy to say the least. It's not really worth the risk and if it breaks with no warranty, well your 500 in the hole. It's a bad gamble...
2. RX 5700 XT is great. I personally like the ROG STRIX and Sapphire Nitro versions the best. It can run games very well at your res and refresh. Heck mine runs 4k on max at 60FPS/Hz it's a stable card and it almost never has any thermal problems.
3. 2070 is ok too. Little more spend and honestly pretty balanced power wise it can easily be considered the RX 5700 XT's equal. Its fancy too and if you like sleek this is the card for you.
4. If you want to go budget mode get a 2060 Super. If aesthetically pleasing GPUs and RGB are your thing go with the MSI ventus if not the ROG strix or if money is tight a Zotac. Don't do PNY just don't...
5. Zotac is cheaper than the others. They also make good stuff. I run one of their 2080s in my video editing rig. Don't be afraid to go with a Zotac GPU.
6. RGB. If you just want something cool go with a 2070 or 2060 MSI Ventus OR the Sapphire Nitro RX 5700 XT.
7. NEVER GET A BLOWER CARD
There you have it.