The MX400 is speced higher than the old MX but there is basically no difference in speed. It's not the core that's holding back the MX chipset but the memory speed, so the MX400's higher core does nothing (maybe 1 or 2 fps in some games). The extra 32 megs of ram also don't seem to do much since the MX runs too slow at resolutions that would need the extra 32 megs to make much of a difference.