I just tried out the new PCSX2 playground because I heard it had a fix to make Persona 4 completely playable. However, even though I set it up exactly how I had it in revision 396, all games are taking massive speed hits. I'm talking massive. 300% or more...places where I got 120+ FPS in FFXII, for example, now don't even run at full speed.

Am I not setting something up right? Am I missing something? Please help...I want to play this new versions as it has a lot more options. I'm wondering if I just overlooked something.

its because of speedstep i think. Try disabling speedstep in your bios it worked for me.

I get the same speed still, if not a bit faster (rev 441).
As Qwin suggested, check your power saving features of your pc.

That's weird, speedstep is enabled for me, and the performance with pcsx2 is fine.
I have also a program called "GIGABYTE Dynamic Energy Saver" provided with my motherboard,
which have a great impact on performance, but I just don't install it.