Cacko can run X apps if you install X/Qt (and necessary dependancies the app might have), the performance will depend on the app and what you are comparing it too - it won't match your Athlon XP 1800+ desktop performance - but generally I've found most apps to be usable but the load time can be quite considerable at times.
Never tried PDAX rom form more than a few hours as they don't have a decent Japanese input method so I can't do comparisons for you sorry.
Stu