Why do some motors have high rpm while other have low even though having same power consumption
The speed of a d.c. motor is given by 

$$ N = \frac { V - I_a.R_a}{kφ} $$

where 'V' is the applied voltage, 'Ia' the armature current, 'Ra' the armature resistance, 'k' a constant based on the number of poles, the number of conductors and number of parallel paths in the armature and 'φ' the flux per pole. 

That speed could be either increased or decreased with the use of a gearbox.

The varying characteristics of motors are the result of design considerations made by the manufacturer over which you, as the user, have no control.

Should you have access to the armature and field terminals, the motor speed may be increased beyond rated speed by reducing the field current and consequently the torque. Likewise, the speed may be lowered by reducing the armature voltage keeping the field voltage constant.