You'll have to make the decision of wether its worth it or not on your own but I can tell you my NP550P7C, which has an i7 and 650M you are looking at, outperforms a friends Dell with the i5 3210M and 650M by about 30 - 35% in terms of FPS in games and benchmark scores.
Side note, I just remembered that his Dell has the 650M with GDDR5 instead of GDDR3 that the Samsungs come with, so the i7 upgrade probably accounts for a bit more of the performance boost than 35%.
I think you should buy the i7 model as it will good for long run as ur major use is Gaming.It will be better for upcoming games. Rest it depends on ur budget. I too planning to buy this i7 model and had searched a lot about ,compare performances,read reviews and it is performing Excellent according to users.