As Dick states you will get more pressure with a smaller M/C..., but it comes at the cost of pedal travel. It seems that the smaller the M/C the better but if you hit the floor before the brakes lock..., not so. So, if you go with unboosted brakes and want a stronger feel go prudently in your downsizing. There are likely sizing tutorials somewhere on the internet but the "math" does not translate into "feel" and my assumption is it is kind of a trial and error process of the average man.