The limitation in braking performance on the Mirage is the tires. Bloodehunter touched on this a few posts back.
Yes, the master cylinder is adequate. The rest of the braking system is adequate. Its the tires that stop the car... and they could certainly be better. But, they were chosen for their economy characteristics.
Here's one of my favorite sets of articles on braking. Written by a brake system engineer and amateur racer. Pretty cool guy, and a great read for anyone who wants to learn the basics of braking system physics without getting too deep.
http://www.teamscr.com/the-book/samp...p-the-car.html