It does, indeed slow things down quite a bit. In contrast, Open book 2.X was greatly assisted with the use of Accupage2. Please note, if you have an HP ScanJet 2CX, the Accupage driver may prevent the scan head from seeing all 14 inches of the flatbed. This won't be a problem on other scanner models. You may find, as I have, that Autocontrast is of much less value than it used to be.
Normal contrast works very well in most situations.
That's all the tweaks I know of for right now. I'll try to make other ones available as they become known to me. Also, Arkenstone will eventually publish an official list of tweaks. The tweaks do not have the same result on every system. Arkenstone, from what I understand is trying to make a more systematic document that can guide you in knowing which changes will help the most for a given configuration.