I'm not personally involved with any mojoportal sites getting 50,000 page views/day, but that doesn't mean they don't exist, very few users ever share any traffic data wth me.
Capacity planning is a difficult and time consuming task to really do it right and arrive at sepcific numbers. I have an article here with links to more information about capacity planning:
However, I will say, that I would expect a sufficiently beefy dedicated server with just your mojoPortal site running on it should in my opinion be able to handle that much traffic. As with anything in life, your mileage may vary. Also if you build your own custom features that plug into mojoportal for this project, the performance of your features will matter just as much as the performance of mojoportal.
Hope it helps,