Choosing a graphics card for a given monitor setup

Hi, I've recently purchased two LG Ultragear 27GL83A-B monitors after finding them barely used for a really good price. This came as a bit of a shock to me; I wasn't expecting to suddenly be driving 2x 1440p 144Hz monitors (quite an upgrade from my 2x 1080p 60Hz HP E232s I've been running for years). I'm midway through building a new PC (5600X miniITX SFF PC in a Dan A4 v4.1), and this has really thrown me on what graphics card I should be looking to get. How do you figure out what tier of graphics card you need to run a given monitor resolution and refresh rate? I've really tried googling, asking on discord servers, everything I can think of, and there don't seem to be any published guides on display/GPU pairings and what level of card can run 1440p 144Hz monitors comfortably.

Also, for gaming, how much does having a second screen that's not being used for anything more than discord/web pages affect your GPU load? I've been pretty confused, because some people have been saying a 3060ti can run 1440p 144Hz comfortably, while others have insisted I'll need a 3080. I generally play older/less taxing games like AoE II DE, Opus Magnum, Factorio, Stationeers, Among us, Project Winter, Human: Fall Flat, Tabletop Simulator, to give some examples, as well as 2d and 3d work in Paint.NET, Blender, Fusion 360, etc.

Thanks in advance for your help figuring this out!

Just about any GPU review will answer the question - look for performance results at 1440p and see if the fps is good enough for the games you like - with freesync you don't need to go to a whole division of the 144hz, just aim for whatever fps you prefer.

However if you're interested in games that aren't covered in reviews you'll have to do a bit of deduction and guesswork - using your current system try some games (usually there are free demos) or free benchmarks that are covered in the modern reviews and compare them to the games you are interested in. Then look at the GPU reviews and see what the scale up is for those games, and apply a rough scale up to your games.

It's not very accurate, but it's something.

Made up example:
Your existing system plays oldRtsTitle at 30fps 1080p, and benchmarks modernRtsTitle at 15fps 1080p
You look at GPU review site and find it benchmarks a modern system with a 6700XT and concludes modernRtsTitle runs at 45fps 1440p.
You can guess therefore that if your oldRtsTitle scales, it'll run at 90fps on your new system with a 6700XT, which is more than enough for you and you're happy with a 6700XT.

Awesome, thanks! That gives me quite a bit more to go on. I'm surprised that there aren't more generalised recommendations out there, for instance something like: For decent performance and framerates in the range of 100-144Hz at 1440p across moderately demanding recent games, select an RTX 30?? or above.

Also, did you have any advice regarding second screens and the performance impact they have?