I think the speed can be increased by reducing the output resistance of the circuit.
This inturn leads to reduction in gain which can again be increased by increasing the transconductance by choosing appropriate way . ie either by increasing the aspect ratio ( frequency of operation may be affected but good current matching possible) or by increasing the overdrive voltage.
If someone feels I am wrong,, i request the to reply and correct my mistake.
thanks,
Muralikrishna
KPIT Cummins Infosystems Ltd, INDIA