In theory, we would actually expect the Tegra 2 to be slower on tablets because of higher 1280x800 resolution. This is not the case based off the (subjective) opinions of users.

I do recall that when the Atrix was released in Canada and I played with it in stores, it subjectively felt significantly slower than my Samsung Galaxy S variant, despite having an ARM Cortex A9 processor that is about 30% faster clock for clock (and that isn't even taking into account that the Tegra 2 is dual core).

I recommend trying to flash other ROMs at this point. Motorola does a pretty terrible job of coding to be honest. Samsung isn't too great either. See if there are any AOSP or Cyanogenmod based ROMs out there.