The extra inch of booster diameter will add a considerable amount of stopping power (makes the driver's leg stronger) but consider this- - - -ANY BOOST AT ALL IS BETTER THAN NONE! The length and leverage of the pedal will probably have more of an effect on stopping power than the diameter of the booster.

Be absolutely sure you build a sturdy pedal pivot and angle brace it well- - - -the firewall is way too flimsy to anchor a pedal and master cylinder without lots of bracing.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!