To sum up what my investigation came up with:
- The game engine is old, buggy. BAD. Perfect World Entertainment uses the very same, very old codebase engine for every game of theirs. It's the same with Perfect World and Forsaken World. The engine only uses up to ~30% CPU and ~30% GPU , no matter if you have an Intel, or AMD, or nVidia or ATI ... doesn't matter. It'll lag, even on a Core i7. (I have tried.)
- Disabling VSYNC (due to the buggy engine) can make a huge performance increase, HOWEVER, you can burn your PC if it's capable of overheating. (VSYNC keeps the max framerate at your refresh rate, i.e. @60hz/60FPS.)
Aaaand that's it. PWE is not likely to upgrade the engine, so DON'T buy a new PC just for this game.. or any PWE game. Go for a simple monthly-paid MMORPG which is optimized (at least well-written). The money you would save on F2P and your new PC is enough for a few decades of monthly subs and expansions.