... and higher power consumption, more heat generated, therefore heat sinks needed and more space, and thermodynamics. etc ...

I have been using Cygnal devices for a quite a while now. These are pretty fast indeed (1 CLK/instruction cycle), yet they consume very little power. I have measured about 15 mA @3.3V and 18.432 MHz. That does not exactly call for a heatsink .... :o)

Rob.