Occasionally a 1" smaller diameter rotor is used on the rear but the argument is generally for weight savings rather than performance. I've used 160mm, 180mm and 203mm rotors on bikes but always with the same front and rear. Matching levers and calipers too.
Of course the majority of possible stopping power comes the front since mass shifts forward as you decelerate which unweights the rear, but when riding off road both brakes are very important to maintain control over loose & unpredictable surfaces.
Most MTBs have either 2 pot or 4 pot brakes. The Stealth calipers are far heavier duty than most, with 6 or 8 pots. The Stealth's master cylinders are the same front and rear for both brake options. If you don't want to lock up the rear, font pull the lever too hard.
An interesting aside: On MTBs I brake with 1 or 2 fingers as do most riders. When I took my motorcycle license course I was taught to use all 4 fingers always on the front brake lever.
Cheers, Abraham
(in rainy Jerome, Arizona at the moment)
Sent from my iPad