Personally, I always save it as an extended 32-bit (with mipmaps disabled), so that it doesn't lose quality (in case I need to make adjustments). After you're certain that your repaint is 100% done, you can then resave it as a DXT3, which will compress it somewhat, and give slightly better frames. Resaving as a DXT3 isn't really necessary unless performance is an issue, though. Hope that helps.