pcsx2 emulator suddenly became very slow

The fact that it's always idled around 45-52 probably means I shouldn't overclock. I just used the Intel Burn Test to see what my cpu goes to on heavy load and it went above 65 without overclock. Read up on your motherboard and how to overclock it.

While sometimes you can OC your CPU itself, the frontside bus is the easiest way to overclock generally and provides a CPU+bus speedup (whereas the clock multiplier is only CPU). Figure out a CPU stress test to run, run it, check temps, overclock, run, check temps etc. I think the general way to do it is to go in 5% increments while checking temperatures (and check temps before doing it too). I am the coolest person ever with my pirate chalice. You might get hwmonitor to check your core temps as you go. You shouldn't have any problems going up to 2.8 on stock.

If I were to do it, what is a safe level that won't leave me worried about my CPU burning up mid-game?

It does have g0 I believe, and I've never overclocked the thing out of fear of breaking poo poo.

Pcsx2 emulator suddenly became very slow