The biggest thing to remember when buying a laptop is you will be using the same machine with the same specs for a few years. Most laptops aren't easily upgradable and aside from additional RAM and new Hard drives. It is easy to upgrade most desktop.
As you are likely keeping the laptop for more than a year or two, you need to buy the best hardware you can afford otherwise you will be stuck with a machine that isn't powerful enough to play any of the more graphic intensive games.
So to answer your i5/i7 question. With the processor, more is more. An i5 will be enough to play todays games but in 2 years it might not be. I would not cheap out on the specs. If that means you have to save up for another month to get a better laptop that will be powerful enough until its time to replace it, you would be better off.
ASUS G75V
16GB RAM
GeForce GTX 670 3GB
128SSD+750GB