I'd recommend checking this thread, and fully reboot your iPad + close parked apps if you haven't yet done so, as this can have a significant effect on performance: http://www2.ambientdesign.com/forums...ad.php?t=32970
I have noticed that some apps, when parked, appear to cause a performance decrease over time. However, if none of the suggestions above improve performance further, while ArtRage is a demanding application, due to the amount of data we have to keep track of over most painting applications ( paint thickness, wetness, reflectivity and so on ) in order to simulate real media, we're always on the lookout for ways to further increase performance. Thanks for the suggestion!
Resident Bug-Hunter and Support Guy