@BadGurlEmi Running Sims 4 at 4k will absolutely affect performance, and I'm not sure you could get anywhere close to 144 fps even on a 3070. There's an easy test though, if you'd like to try. The Nvidia Control Panel allows you to tell your GPU to render a game at a higher resolution than your screen. The setting is called DSR, and you can choose the factor that translates to 4k. For example, if your current monitor runs at 1920x1080, choosing 4x as the factor means the GPU will render the game at 4k. Then you can decide whether the performance is good enough for you.
If you need more specific instructions, let me know. But it's pretty straightforward once you open the Control Panel and have a look. I'd suggest only changing the setting for Sims 4, so using Program settings rather than Global settings, so as not to impact your other games' settings.
This obviously won't tell you how Sims 4 will look in 4k, since your current monitor doesn't support it, but the answer there is that it will look amazing, just not necessarily so much better than 2560x1440 that it's worth the hit to performance.