Personally I don't see a comparison when up against the M4. I was excited for the RCF but that quickly wore off when I saw it at the dealership. Not a fan of the look of the body, the wheels and it doesn't feel like it 'fits' together. M4 by a long shot IMHO even if it's more expensive. This article had it winning most comparisons as well.
I also don't get what Lexus is doing with fuel efficiency.. I feel like my 350 takes too much gas as it is