CF6-50's were always smooth starters, especially when we adopted our PP engineers' recommended method of putting the fuel on at 10%.... Seemed odd at first, but made for a
very smooth start, as the thing would light off at about 15% and, they claimed, the thermal shock was was much less that way compared to motoring to max motor before lifting the fuel cock. Haven't run a -50 for about 10 years now... I miss those beasts! Great engines to work on!
CF6-80's (been fiddling with them since about 1988 or 89, and still am) are also quite smooth during start.... Unless something's wrong of course.
Slightly off topic, it seems a natural inclination for pilots to throw in the fuel at max motor. I have experienced with CF6-10 through 80's that unless high and hot throwing in the fuel above minimum motor just as N1 starts to slow in acceleration saves starter life and is just as healthy for the motor.