I think the overdrive voltage is mainly dependented by the Vth and the transistor where it is used. I think 10-30% of Vth is good for current mirrors and 8-20% for cascode transistors.
overdrive voltage should be greater than 100mV for transistors to operate in saturation region. usually designers keep overdrive volatge around 150mV for safer side.
For example, in my Folded cascode, my input pair is a PMOS, i have to take Vov =0.15 (0.2) for all the transistors? for the input pair, the current mirror and the cascode??
And, with a folded cascode what is the best output swing i sould take?
For Vcc = 5V,??
For Vcc = 1.6??