REALZEUS:
Since when do you have to wait forever for the revs to build in an M5, not to mention other NA sports cars? 
It's just a simple matter of engine architecture, all high revving NA engine has the same deficit, they don't make much power lower in the rev range, they are all tuned to deliver power higher in the rev range, most if not all of the great NA engine don't make power until at least 4k-5k rpm.
Even the current V10 M5 suffers the same fate with the 5L engine, drive a M5 and a CLS55 back to back and you will see how the M5 is lack the instant low end power of the CLS.
That's one of the reason BMW is going the Turbo route, boasting low end power while retaining absolute power output, I would expect the new M5 engine to be a gem in delivering explosive power up and down the rev range like the engine in the X5/6M.