6x Eyefinity? hahaha... now even mild-core Eyefinity gamer able to enjoy bigger Eyefinity, yeah~~ Dell FTW

Just to answer your few question to clear your doubt.

Backlight bleed issue can happen to all monitors, although this isn't noticeable at bright pixels other than dark black (no light), this usually only happen during very dark movies, if there's too much bleed, you can always call up Dell to exchange another, well since it's door-2-door so you won't need to worries about all those petrol, parking, etc.

8ms is actually quite fast, unless you're playing those super high-pace shooting game like Counter-Strike, Sudden Attack where you need to turn really quick and still able to see the surrounding clearly, otherwise the 8ms advertised is darn good (and it's no lie, it's actual G2G 8ms, measured by professional reviews).

From my experience, newer shooting game does not really need those 120Hz any more, most of them is getting it for the 3D, other than that, high-pace shooting is only for those who wants clear image at very quick games (less blur effect).

As for the Alienware overdrive, not too sure about the quality lost, though I don't think that's much concern if you're playing those high-pace game and only worry about getting shot at then looking at those eye candy??

Depends on what you looking for, the LG equivalent (IP236 or something similar) is cheaper by RM20~50.
Dell offer better warranty service and better features beside provide IPS panel, for me those features worth more than what you bargain for so Dell option is the better recommendation, but some said otherwise, it's up to you to choose.

Usually get Brightness to highest comfortable level then tune the contrast, too high of contrast will destroy the neutrality of the color (overly vivid).
Lag in terms of? Does it happen when you watch offline video such as those video files inside your PC?
Have you tried other monitor? Using VGA? Perhaps try DVI cable?