The reason why I don't want to use VU Cycle Stealing is because it slows down some games and also, most of the time (SotC being one of the exceptions), it creates a phenomenon known as 'false FPS readings' (I think we should find a better name for this).
Without getting too technical on you, the way VU Cycle Stealing works is by not emulating the PS2's EE chip while VU1 microprograms are being executed, since the EE is just sitting there idling. So basically VU Cycle Stealing frees your CPU from emulating the EE during VU1 microprograms, thus speeding up VU1-heavy games
like SO3.
The reason why this speedhack sometimes causes 'false FPS readings' (or whatever it should be called) is because the way PCSX2 implements this hack is by skipping cycles on the EE by some arbitrary amount, based on guesswork on how long the VU1 microprogram will take to execute. Sometimes this guess is wrong and the hack skips more cycles than what were actually spent idle. This translate to slow downs. The problem becomes even more noticeable when you have EE Cyclerate turned on because you're giving the EE even less cycles to work with.
Anyway what I'm trying to say is that sometimes PCSX2's 'FPS counter' might be showing 60 'FPS' (since the emulator is running at fullspeed), but the gameplay itself is slowed down, and this is caused by VU Cycle Stealing. Try it. Bump VU Cycle Stealing up to '2' or '3' and you'll REALLY start to notice the slow down in the game, even though PCSX2 is reporting 60 'FPS'. Just because PCSX2's 'FPS counter' skyrockets with those speedhacks doesn't mean the gameplay is actually running any smoother.
EDIT: I think this is why laymen refer to this phenomenon as 'false FPS readings', because PCSX2 is saying 60FPS but the game is clearly not running at 60FPS. If you notice though, the music is not slowed down (since it's handled by the SPU2 chip, not the EE chip) as you'd expect it to be if the emulator really wasn't running at fullspeed. That's because the emulator IS running at fullspeed. If it wasn't running at fullspeed, neither would the SPU2, so the music would slow down.
P.S. What program is telling you that all 4 of your cores are sometimes hitting 3.9GHz? Is it that overlay that I see on the screenshot? BTW I love the name of your RAM. 'leggera' makes me think of the Superleggera versions of some Lamborghinis. XD