I sent an email out just now to you on this topic. It sounds like the problem you're experiencing is the gap between the stylus and the end of the stroke, which is due to the way ArtRage handles the way paint interacts with the brush head and canvas.
As a test: Paint a slow stroke but at the end of the stroke, stop moving and don't raise the stylus. If the stroke doesn't move any further when you stop moving then the problem isn't latency but the gap. Raise the stylus and if the stroke connects to that point then it's working as expected.
The solution at this point is to paint strokes naturally and not worry about the gap because it will be filled in as soon as the stylus comes up.
If you paint a rapid stroke and it is lagging behind, I'll need details on the speed of the modified Mac you're using.