It seems unlikely that Start8 would benefit from GPU acceleration, which is best-suited to such intensive tasks as 1080i/p video playback/decoding etc. You must have some other problem (with the UI responsiveness).
About Windows 8 being slow to start, I agree but that's probably not Start8's fault. Windows 8 fools you into thinking it starts fast, because indeed the Title screen and the Start/Metro UI & apps are available very rapidly (much faster that Win 7's desktop). However, the Desktop boot-up (and the relevant applications) take quite a while to load, equal or perhaps even longer than 7.