A term you don't hear much anymore is optimum cylinder displacement. It was big in the 50's and 60's, especially in F1 when only the engine displacements were fixed by "the formula", and the numbers of cylinders weren't. Some teams, like BRM, chased high rpm HP, so their solution was a 12,000 RPM, H16 motor with 187cc cylinders. Others, like Climax, thought it could be done by low end torque alone, so they used 4 cylinders at much lower RPM.
Some would say the magic figure for a modern automobile motor is 500cc's per cylinder, in a slightly oversquare configuration, for the range of RPM that most (non American) street motors will see. This may be one reason our 4.0 litre V8's are such little jewels, why the 2.0 litre I4 Honda motors, and 3.0 litre L6 Supra motors are so popular, and why BMW's 5.0 litre V10 is too, and why there are a number of 6.0 litre V12's now.
The thinking that the greater the number of cylinders, the longer they take to rev is pure nonsense, and if anything, the inverse is true. It's all about the rotating and reciprocating mass in each cylinder. (And of course, how big/heavy a flywheel they have!)
Would anyone try to argue that a 1200cc 4 cylinder Honda motorcycle engine doesn't rev as fast as a 2 cylinder Harley with the same displacement?
Similarly, I've not heard too many 6.0 litre Ferrari or Lambo V12 owners complaining that their motors take longer to rev than the 6.0 litre small block chebbies in their Suburbans......
The current crop of 12 cylinder engines from Germany going into their luxury cars are built for smoothness and low end torque with "some" high RPM capability, and as Peewee said, the V12 sound and status for their owners. No they're not high RPM screamers like Ferrari's, because they weren't designed to be. These design goals are what probably create the impression in people's minds that V12's are slugs, but it's not inherent to a V12 configuration.
BTW, ask me what an expensive PITA it is to take a BMW V12 motor, designed for smoothness and torque, and try to rework it to make it a screamer.......