Hey there,
Well, that totally depends on what games you are playing. Some games can take advantage of more cores/threads. Others, not so much.
With a boost speed the same on both CPU's, for games that only make use of single core speed, then it will mostly be a draw, with maybe just a few FPS difference. However, with the 6c/12t CPU you may get much better avg FPS, 1.0% lows, so games often feel smoother with more host processing resource.
Here's an example of just a few games:
i3 10105F vs i5 10400F – Test in 8 Games - YouTube
Depending what games you play it could be worth it, by selling your current CPU to offset the costs. Might give you more oomph in newer games which expect large core/thread counts. Certainly most online first person shooter games, with 32-64 players, the extra cores/threads make a big difference.