I'm sure the M4 will be underrated - that I don't doubt. I'm also disappointed to find out that earlier reports of 480 hp has now become "at least 450". But, the new RC-F will handily beat any stock E9X M3 since the revised IS-F and E9XM3 became a dead heat after a few suspension revisions.
Right now, we are just speculating. Nobody knows the exact specs and how the cars drive. I'm not in the market for a new car anyways. I'm just enjoying all the different performance cars flooding the market.
Even though the RC-F can't be tuned or FI, at least one thing I know is that they probably left 50+ hp in the restrictive cats and exhaust. My 6 year old IS-F has just headers and exhaust and is already around 470 crank.
BTW, for all of you guys that always say that the 8 speed auto sucks, probably haven't ever driven the IS-F 8 speed in manual mode. Under manual mode, you really can't tell the difference between PDK, DCT, 8 speed auto. I can't tell and it upshifts and downshifts almost the moment I flip the paddle. So, what's all the negativity about the tranny?
So, perhaps the RC-F will be slower but if it wins comparos based on steering, chassis, fun-to-drive, etc.. It'll just be like the old days but reversed when the IS350 handily beat the 330i (a couple of years before the 335 came out).