Tablet PC as a art pad: not as great as I expected

The more I use my Tablet PC as an art pad, the more I realize that it's far from a great tool. Applications that specifically wrote for Tablet PC, like Alias Sketchbook Pro and ArtRage, works great with Tablet PC. But other tools like Manga Studio or Photoshop has serious delay problem. At least I thought it was just my machine, but after reading some forum posts, like this, and this, and also this. On my Tablet with Wacom Graphite 4, I have zero lagging problem. So I guess I should with using Tablet PC mainly just for sketching.