GTX970 upgrade options

[TNGengar]

So I've been holding out on upgrading my GTX970 now for a good few months, waiting primarily to see what came out of Navi. After seeing the RX 5700/RX 5700XT, I feel I have 2 options.

I've always has NVIDIA cards but bought a freesync compatibale monitor just before christmas 2018 and so would like to benefit from the feature by getting an AMD card.

I'd like to budget myself to around £300 and don't mind buying used. I've been thinking about a Vega 64 but wouldn't mind an RX 5700. I'd like to be able to play on medium settings at 2560x1440.

Any suggestions would be amazing thanks.

Other main system specs:
i7-3770k @ 3.9Ghz
16GB DDR3 @ 1600Mhz

 

[TNGengar]

From what I’ve heard it’s dependant on the monitor whether adaptive sync works? Going by the NVIDIA website, my monitor isn’t compatible.

 

[TNGengar]

I’m playing at 1440p on a 144hz monitor with most settings on low (I’d rather have higher FPS over graphics quality) and only got a slight oc (see photo).
https://i.ibb.co/Yp5kDPV/Capture.png

I mainly play PUBG at the moment and average around 80fps with textures and AA on Ultra and all other settings on ultra low.

 

[TNGengar]

Thought I'd update to put this at a close and say after much thinking and research, I've decided to go with a new Sapphire Vega 56 Pulse at £269.99 fro OCUK.
Thanks for the responses guys.