gosh ..the right expression is:
f = ( 2*PI*(Rs*Cgs1 + Cgd1*2*Rs + Rd*(Cgd2+Cdb2+Cl) + 1/gm2*(Cdb1+Cgs2) )-1
and with the values f = 2.08EE+08 Hz.. very similar to the CS's one
you sad that you got a corner frequency of 315 MHz for the CS amplifier, and a corner frequency of 984 MHz for the cascode.
did you get these values using the simulator? they are really very different from the values obtained from manual calculations...