the size of transisitors is based on the gain and BW. basically we want to get tahe gain as larger as possible. usually, gain equals gm*Rout. so you should increase the rout and gm. the cascode configure's rout is inverse to the biasing current, and propotianl the Longth. for gettting the larger Rout decreasing the biasing current of out colume is a good idea. meanwhile, you need increase the input biasing tail current to increas the gm. but too large ratio is very good. some experencided designer advizes the ratio should be 3~4.

best regards,