what Bore master cylinder

I am running manual brakes with 13 Baer disks up front and 11.75 Wilwoods out back. I want to upgrade my Autozone manual master cylinder. Its a dual reservoir. I have a proportioning valve-adjustable I use for the rear brakes. All work well but i do not trust the Autozone Master cylinder?
When you look at aftermarket master cylinders you can purchase them in various bore sizes. 7/8. 1inch ect....
How do I determine what bore size to buy? The bigger the bore the more power i have and is it that simple?