if you're on windows, downgrading to painter IX (or even earlier) would solve many performance woes.
also, check your memory usage (should be somewhere in painter preferences, I don't remember what tab exactly it is on windows) - on 64-bit os, windows painter should be able to utilize more ram. on mac, it's currently capped on 2 GB.
and try reducing number of cores, allocated for painter, to 1 or 2 if you have more.
on the fourth day of glitchmas my painter™ gave to me
four random crashes, three broken brushes, two system hangups & one corrupted workspace