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 'hold back' the graphics card, due to the performance differences (Processor not being able to keep up with the faster graphics card).
Plus the differences in Graphics memory 2GB's to 4GB's makes a considerable amount of difference in games. The 4GB model graphics card would be beneficial.
Overall, I would recommend the GTX 950M with the i7-6700HQ, if possible + would be worth it in the long-run.
Hope that helps,
SM