the MR and the GSR is the same damn car for the most part. the differences are the MR gets the 6spd tranny, bilstien shocks, bbs wheels and some other small stuff. There is no extra power in the MR then a GSR. The motor is the same. The suspension is the best part and the wheels. but to me that is not worth the extra cost. The 5spd tranny holds up better once you start modding and putting down some good power. Neither car has more problems then the other....they are both great cars but you have to determine your goal for the car so you dont buy a MR and decide you need a 5spd for racing or power....that would be a waste. the suspension can be bought aftermarket and even lighter wheels can be had for way less then the bbs's. Hope this helps if you have any questions post them up.
If it was me go I would hands down buy a GSR and spend the difference between the GSR and MR on some tastful mods.