Even though Jpcsp is written in Java, it can already reach 100% PSP speed on a lot of commercial games... and the emulator performance is constantly increasing.
Jpcsp takes full advantage of dual-core processors, matching the PSP dual-core architecture. Even a quad-core can give a small performance improvement by leaving free CPU cores for the Java JIT Compiler and the graphics cache.
NVIDIA graphic cards are fully supported and Jpcsp can take advantage of powerful GPUs. Problems have been reported with ATI/AMD graphic cards: keep you Catalyst driver up-to-date as new releases might fix issues.
The project is still a beta release, but currently more than 600 games are already playable. See the list here