Arma3 will benefit somewhat from X3D but as an former Arma3 player with 5800X3D I can tell you that there are many instances where the X3D will just not be enough to have a good performance.
In SinglePlayer it is usually fine but in MP you will still see severe frame drops on big cities with many players.
The main bottleneck is the game engine, not your HW. Also upgrading for 3FPS?... what thoughtprocess is that?
I'd say upgrading to X3D is worth it... just not for Arma3. There are plenty of games (for example most battleroyales) where it makes a big difference though.
If you want almost the same results as liquid metal with no risk then just stick to using PTM7950.
Besides, bad application or bad re-lid will nullify any benefits of liquid metal.
Some loads still benefit from higher clocks and don't draw much power... in which case power limit does not make much sense but sometimes the card just draws more power when it's available for no particular reason so this makes it more difficult to do so. It's quite a rare scenario though.
I prefer power limit maxed out + undervolt + OC + FPS cap... more efficient in most cases.
NVIDIA:
RTX 4070 or better
AMD:
RX 7900 XT or better
Also it depends a lot on what games at what settings. But you will not be able to avoid upscaling in most modern games.
IDK, these seem like something went seriously wrong. I'd run a RAM test to make sure it's not the memory corrupting the system. Check drive maybe as well while at it.