does a 27speed on a bicycle means its faster than a 21speed bike?

[wle ņ|ã??? ????????]

no
speed is up to the engine - you
wle

 

[Ron Michael]

I was looking for rear derailleurs and saw a 9 speed one and a 7 speed derailleur. and if it has 2 more gears, would it fit any frame of a mountain bike?