Lenovo Y510P or Lenovo Y50?

Which one has better performance and less expensive?

Added (1). Lenovo Y510p GT 755M SLI

Added (2). Lenovo Y510p GT 755M SLI

Lenovo Y510p GT 755M SLI: $1,076.77
Lenovo Y510p GT 755M SLI: $900

Here is the price of above two laptops on Amazon. Both if these laptops are best in this price range and both have best configuration. But Lenovo Y510p GT 755M SLI is better than other one.

You can see bellow list, Actually I have seen all the specifiaction of all the models, There are only difference of RAM.

Lenovo Y50 Laptop Computer - 59416738, its price = $1,299.99
Lenovo Y50 Laptop Computer - 59416755, its price = $1,149.99
Lenovo IdeaPad Y510p 15.6-Inch Laptop, its price = $1,079.99
Lenovo IdeaPad Y510p 59385820 15.6", its price = $1,279.49