I can't see the reason for speedstep. The idea that the CPU should figure out what the user needs is, frankly, moronic thinking my (un)Intel.
Automatic speed control is mainly a power-saving measure. It allows the CPU to run at its minimum speed when idle or lightly loaded, preserving battery life, spring into full speed as needed, then return to minimum speed when the task is done. It also helps lower system temperatures, maybe even enough to turn off the fan, lowering power consumption even further.
Complete manual control over the clock speed can have undesirable consequences, such as the laptop eating through your battery charge just because you forgot that you kept the speed at maximum when you're just typing a document. Temperatures will be higher too.
A compromise could be made: keep Speedstep, but have the ability to manually set the max speed. You don't even need new buttons-- you can use the Windows key + the volume up/down buttons to set the max speed. With a little programming, this could be done.