To clear up the misinformation here's a grid of the features of all three:
http://www.mitsubishimotors.com/MMSA...pecs.jsp?t=all
All IX's have ACD now (active center differential) [DCCD is for subarus] {no US Evos have AYC}, the turbos and engines are all the same on the IX's but are a significant upgrade to the VIIIs (slightly larger turbo and MIVEC).
The RS and MR both have aluminum roofs. The MR's biggest features are the 6spd transmission, BBS wheels, Bilstein dampers, and areo parts (vortex generator, wicker bill, etc). The MR is probably not worth the price. I had a hard time deciding between the RS and MR and if I hadn't gone into Brookdale and gotten a good deal I probably would be driving an RS now.