The dual screens does not up his resolution. I doubt he will be gaming simultaneously on both screens at once and for non-gaming purposes any card can handle two screens.
That GTX 460 is a good deal but personally I would get this one for the same price(though $10 more after the rebates.)http://www.newegg.com/Product/Product.aspx?Item=N82E16814121391
It is a better brand with much better cooling. It should also overclock very well if you are interested(it's pretty easy to do.)
Another option is this HD6850;http://www.newegg.com/Product/Product.aspx?Item=N82E16814150516
Also $125 after rebate and promo code but it comes with Dirt 3 and Shogun 2. Even if you aren't interested in those games they can probably be Ebayed for about $20 each.