What's your max budget? Most light powerhouse laptops are generally expensive so I recommend checking out the Razor Blade 14 inch laptop (http://www.razerzone.com/gaming-systems/razer-blade/)
it weights 4.47lbs and it has one of the most impressive technical specs of any ultralight laptop.
However, the price is exorbitant and it will run you atleast $2,199 depending on the SSD storage.
MSI also has an ultralight powerhouse it costs $1,699 and weighs 4.37lbs (http://www.newegg.com/Product/Product.aspx?Item=N82E16834152566).
The difference between the Razer and the MSI is mostly the graphics card, which is about a 10-15% performance difference.
Hope this helps
These are probably the lightest and most powerful gaming laptops in the market!