120GB 840 for boot, 250GB 840 for games & apps, 1-2TB HDD for other stuff (or a 500GB-1TB SSD for games, apps, & other stuff)...but that's just what I would do.
Pro costs too much for just an average user to consider it for any sort of beneficial speeds (unless you're a baller and just wanna spend).
Evo is gunna have the benefits of the Pro's speed with the price of the non-Pro, larger capacities, and you get Samsung Magician (IDK if you get that already with the 840 and the Pro).
Honestly if you're gunna use it now, get the 840. If you can wait a bit, wait for the Evo.