Personally, I'd get the BenQ. You have a good video card and should have no problems keeping 120 fps in games, so you'll see the benefits of 120 hz monitor. And you seem to really like the idea.
Also, instead of dropping $650 on that Dell, look into getting one of the Korean S-IPS monitors. Vast majority of people are having great experiences with them (ie no problems), and they're going for ~$400 including shipping. You can get a BenQ AND a 27" 1440p IPS for ~$750.