From what I've read the RTR wheels are a couple pounds lighter per wheel compared to the Brembo wheels. Lighter weight wheels (unsprung weight) does make a big difference. When I get my car (Monday, I hope) I will weigh the Brembo and the RTR although I just had the tires mounted on the RTRs yesterday so the comparison will be with tires.
I do agree with those who have said the wheels do stick out a bit far, but when the axle has been properly centered it's not obnoxious. I'm adding the factory GT500 mud flaps which also reduce that visual distraction. The main benefit in my eyes is that the wider track should improve the handling of the car- wider track means less jacking and lower center of gravity. Look at the BMW competition package for the M3... wider track.
I also believe that it's really only the rears that have the offset "wrong", and there's a ton of meat on those wheels. I'd bet you could have a few mm machined from the back increasing the offset.

 

yes, the rears are out a bit too far. My guess is that they saved money by only buying the tooling to do one offset, and it is for the front but gets by in the rear also.

it is not obnoxious in the rear but like carnut says, the axle has to be adjusted perfectly. IMO the car looks the best lowered, at stock height the rear of the car looks weird with these wheels.

 

Anyone know when these will be back in stock? I placed an order about 3 weeks ago. They seem to be back ordered everywhere.