PCSX2 GTA III PLEASE HELP

Hello there.

I got a cheap PC basically to play GTAs and GoWs from the PS2 while I plan a PC build.

The thing is that I'm having issues to achieve steady frames in GTA III.

Most of the time I get 25 FPS in the EU rom and about 30 in the USA version, but as soon as there is a little action on screen, frames drop as low as 9 and about 15, things go back to normal as soon as there everything calms down.

I've tried different settings for about an hour or more without much progress, but I think this PC is indeed able to handle those games, CPU never go above 45-50% usage while integrated graphics stay at a max of 30-35% usage.

Even if I mess with the settings, I can get 50 fps for most of the time, dropping to about 30 while there is more to render, but those 30 fps really feel like 9-15...

Specs are
Intel 12th gen CPU 4C/4T 16 EUs (integrated graphics), 1,7 GHz up to 3.4
16GB DDR4 RAM.

Only problem so far are those GTAs, haven't try GoW yet.
I even tried playing the XBOX Classic versions and it was just terrible.

Please, help.
I'm running the latest nightly btw.