From the first 100 MHz processor to the first 1 GHz processor was almost exactly 6 years. I jumped from 1 MHz (Commodore 64) to 66 MHz to 333 MHz to 900 MHz (I for get if that's exactly right...It was a Duron). After that it was probably something close to 2 GHz (Athlon XP).
I remember a couple of years after I got my 486 DX2 66 lusting after the Pentium 133/150/166...the MHz sure increased fast back then.