The GSR is going to be the best selling model by far, at 3500 cheaper than the STI you can still get nice wheels, HID's, and a spoiler (though I really like the smaller one) with a little left over. The only sales the MR is going to get is people who want the performance but want a auto, maybe potentially taking some sales away from the STI, but that same number of people wanting an automatic in this class could be very small.
Good to see the STI coming down in price, I wasn't a fan of the styling at first but it has really grown on me. With the STI being faster than the Evo and cheaper than the MR models I think it has the slight edge in the competition.
If your disappointed in the performance of the X keep in mind the last time Mitsu switched body styles the VI was faster than the VII, but the VIII and IX were faster than the VI.