Simple answer, the i7-7500u (Dual-core) is basically an ultra-low voltage processor, ideal for 'on the go' laptops and power saving, with good performance for business/office work
On the other hand, we have the i7-6700 hq, a pretty fast (Quad-core) processor, ideal for performance focused tasks. For example, photo editing, gaming etc...
Additionally, the GTX 950M is a pretty good mid-range graphics card, can play a variety of games at medium - high settings (Depends entirely on the game obviously).
Pairing the GTX 950M with the i7-6700HQ would be ideal, and would allow you to play relatively all games at an average of medium to high settings, with pretty good FPS. However, pairing the GTX 950m with the i7-7500u would bottleneck or...