Only 3 plugins are used by PCSX2 as long as you use an ISO file (instead of an actual DVD media at your DVD tray). These are the Audio plugin (Use SPU2-X) and the Graphics plugin (Use GSdx) and the Gamepad plugin (Lilypad).
PCSX2 will run faster when using a DVD image file (instead of an actual DVD media). Create an image file with Imageburn. Other tools might create corrupted images, or not.
To run a PS2 DVD image file, DO NOT MOUNT THE IMAGE (daemon tools, etc). Instead, use CDVD -> ISO Selector -> Browse, and choose your image file. Note that despite the name "Iso selector", many image formats are supported (iso, nrg, cue/bin, etc). If you followed this, then the "Iso" item would be selected at the CDVD menu, and the CDVD plugin will NOT used (This is OK - PCSX2 will load the image file without using a plugin).
Use SPU2-X (other audio plugins are usually less compatible).
SPU2-X configurations have little effect on speed (at most about 3%, and usually less). If you want the absolute fastest emulation you can squeeze, choose Interpolation - 0 (Nearest neighbor), and disable effects processing.
Use GSdx (other plugins are usually slower and less compatible).
- GSdx Renderer: Use one of the Hardware modes for best speed. Use one of the Direct3D (Software) modes for most compatible visual emulation (usually with negative impact on speed).
- GSdx Scaling/Resolution: For fastest emulation, choose "Original PS2 resolution". Note that while higher resolutions mostly looks better, they might also cause some visual glitches (after all, the games were designed for the original resolution only). With a recent GPU it's possible to use higher resolutions with minimal impact on speed. Using one of the x2/x3/... scaling options is usually less likely to create visual glitches than using a custom resolution. On some cases though, a custom resolution might remove some horizontal/vertical thin lines (Try: 1200x1200). (I usually use x2 or x3).
- "Allow 8 bit textures" might improve speed significantly for some games, and might also hurt performance for other games. Try both modes for each game. (I personally leave it usually on).
- Alpha correction might hurt performance on some games. Try with or without it for each game. (I personally leave it usually off).