For gaming the better GPU will give you more performance increase. Also taking in account that i7-4702mq is already a really powerful CPU and you don't really need anything more powerful than that for gaming, the stronger GPU will give you more benefits.
So yeah - i7-4702mq + gt 750m all the way.
for that amount of money you could get 750/755M SLI + I7-4700MQ
The specs look good on paper but I haven;t seen an actual Lenovo laptop in person in years. My concern is that they still suffer from quality issues and that the case build/materials will be cheap.
The SLI option looks temping but my concern there is the cooling fans will be running at freight train speed trying to keep up with the heat generated.
Lenovo laptops are actually one of the best laptops quality-wise these days!
If you could find the Lenovo y510p for the same price as the other intel laptops, definitely get the Lenovo laptop. You will have to buy a cooling pad for the laptop anyway, if you're planning to play games. So the temperatures will be fine with the cooling pad.