The i7 is literally wasted when used for video gaming. The only (debateably) valuable thing between an i5 and i7 is the hyper-threading tech that is literally ONLY useful for audio and video decoding. Unless you plan to render high resolution CGI graphics for a major motion picture, there is absolutely no reason to spend the extra money.
But when it comes to technology, people are always willing to shell out the extra money for the absolute best even if they aren't going to use even a quarter of the features. Computers with 16GB of RAM? You barely use 8 more than half the time, and the other half I will be seriously impressed if you're using more than 10. But everyone builds up their computers with 16, 32, and now even 64 GB of RAM that they couldn't possibly ever use themselves. It's the same with the processors.
But don't take my word for it mate. I am just regurgitating hours of research. Always do your own research before believing others. Just Google "the difference between i5 and i7," you're going to see the only notable difference is the hyper-threading technology. Then Google "Do I need hyper-threading" or "How do I use hyper-threading" or something similar, and you'll realize that you're never going to use the technology and the extra $200 might as well have been spent on RP.
And, this is a biased statement, Alienware isn't worth the consideration anymore. They were bought out by Dell, who isn't as bad of a company as they used to be, but they are STILL (after all these years) in no way capable of delivering high quality gaming machines, and the Alienware name has been tarnished heavily (though the Alienware name was already kind of degraded after several cases of overheating CPUs, mismatched hardware standards, and horrible customer service... that of course was all before Dell acquired them). Meanwhile, ASUS continues to be my top three favorite brands to buy both computers and hardware from, the other two being MSI and Lenovo.
Ultimately, do what you want. If you want the latest and greatest, even if you'll never use half of the hardware's potential, buy the Dell. But if you want a quality machine that will last you for a long time (assuming you're going to take care of the machine, like not leaving it on for days at a time and never cleaning it) with hardware you're actually going use (though still less than half the capacity with the specs on that thing, but while you shouldn't buy an expensive machine you won't even use 1% of the power of, you also don't want to aim to use 100% of a computer's potential.. I aim for around 50% during regular usage when considering specs), then get the ASUS. I personally guarantee you'll be happier.