Whats in question is is your 650m actually turning on during games, i.e. is optimus working correctly,
Disabling intel card doesnt answer that question in this case.
Best way is to download GPUz, at the bottom set the videocard to the 650m, go to the sensors tab, and you will see a GPU Load %,
with that open in the background, run your most played game (the one your not happy with) for a 5 mins or so, then exit it or alt+tab out of it, you will see the history graph of the load % in GPU will either be flat and low over the past 5 mins or it will be high and spikey.
High and spikey= your card is either too slow for your liking, or is underperforming (overheating etc)
Low and flat= your optimus isnt turning on the 650, in which case it will be fresh install of drivers (which i think you said you tried) or nvidia 3d settings forcing optimus on for the game your playing, or the videocard is faulty and optimus cant switch cards.
It could also need a BIOS update, as with alienware these sometimes come with a VBIOS update built in which can help with cooling etc.