It depends on what you want. Stock power brake master cylinders were 1-1/32", the manual master cylinders were 15/16". The larger bore moves more fluid faster, so you get a higher, harder pedal (which is why they were used with a booster). The smaller bore results in more pedal travel and a higher line pressure, and I find the longer pedal stroke makes it easier to control the brake engagement. A 1" bore would be closer in feel to a 1- 1/32" MC than the 15/16", and personally I like the 15/16". The one I use is sold by Dr.Diff, it's a late model aluminum MC that he sleeves down to 15/16" and modifies for the stock manual push rod.
