PS2 has had a lot of rapid advancement in emulation over the past few years; there's still some problem titles (MGS2/3, the Ace Combat series, the God of War series) that require extra beef to get to fullspeed, plus a few games like Silent Hill 2 and 3 that are a little glitchy regardless of your hardware unless you enable workarounds, but past that, if you have a quad-core that's either Haswell or later (for Intel) or running on some form of Zen (for AMD), and an even halfway decentish GPU, you can run 95% of the library fullspeed without issues.