The Tesla P100D's dual motors combine for 760 horsepower, which would be more than enough to sustain 200mph+ with proper gearing and tires. By comparison, a Lamborghini Gallardo achieves a top speed of 202mph with just 562 horsepower. The Tesla's motors redline at about 16000rpm, which at the 9.7:1 fixed gearing ratio corresponds to about 155mph. If the gearing ratio were halved, the low-speed acceleration would reduce but the top speed would go up dramatically.
True, at 200mph the P100D battery pack would only be good for about 40 miles. But gas supercars don't do much better. At top speed, a Bugatti Veyron can burn through an entire 26-gallon tank of gas in just 12 minutes (51 miles).