NO! steer clear of the Motegi MR7s. Those are some heavy, heavy bastards.
Yes, you will notice a considerable drop in performance when you add big, uber weighty wheels.
If you're stuck on motegi, check out their "traklite 2"s. the 15"s are 10.5 pounds each, the 17"s are 14.5 pounds.
in comparison, a 17" MR7 = 25.5 pounds each.