[blykins]

On a linkage system, like an old Ford with a Z-bar, there should be 1/4" of space between the TOB and the pressure plate.

On a hydraulic or cable system, the TOB should lightly rest on the pressure plate.

Now with that being said, I would make sure that your hydraulic line is bled perfectly so that you can get all the travel you need.

Also, if you go to a larger master cylinder, the amount of force that you'll need to put on the clutch pedal to fully engage it will go UP. The amount of travel needed to get the same slave cylinder movement will go DOWN.

If you go to a smaller master cylinder, the amount of force that you'll need to put on the clutch pedal to fully engage it will go DOWN. The amount of travel needed will go UP.