2D games or extremely low polygon games like Disgaea, you can expect anywhere from 3-20 FPS.
For intensive / normal games, you can expect with Recompiler apx 0.01 FPS to 5 FPS. Depending on your rig.
If your looking for fast PS2 gaming, go buy a nice silim line PS2, they're only around £120 in the UK, and in the US around $100-150. Or come back in 2 years time, with a brand spanking new top of the range machine, and give it a whirl, you never know, you might just get 10 fps
