cpu voltage. Decreasing it will hinder performance?

Apparently my Motherboard has an !enable intel speedstep" option, that is supposed to lower and heighten the cpu voltage according to need.

With it disabled, the voltage is at 1.31 to 1.33v, and my processor reaches 55ºc of temperature.

With it enabled, the voltage is at 1.18 to 1.22, and it reaches only about 51ºc temperature.

So, it seems enabling it might be good, for a number of reasons, but I'm in doubt about performance. Will this voltage decrease degrade performance?

The cpu is a pentium 4 sl630 3.0 ghz, rated by intel to have an optimal voltage of 1.20 to 1.40 volts. So, will having it run at 1.18 at times be bad for it?