if you're getting an 6950 (which is a very good card) try to research into one with a BIOS switch and if its compatible to flash cause then u have got yourself a 6970 from a 6950 . i personally like the Twin frozr as the cooler is quiet and keeps the card itself cool. im not 100% if its a PCB model so it might not be able to flash but you could OC it very well with that dual fan cooler
Yeah the 2nd monitor is great i've seen it in a shop but i hate monitors with speakers for some reason, even if i won't use em
Now, about which Gpu to get... I got XFX 5870 and its perfect, but i've heard so many people saying they have problems and have to RMA. Xfx offers lifetime warranty though and you always get a new one that works at the end of the day. However, I would recommend to buy the MSI cause of the fans system and the ability to fully use MSI afterburner to tweak the card. MSI has never let me down on any product i've bought in the past years.
unless you plan on gaming at res higher than 2560x1600 or using eyenfinity, save your money and see if you can get the 6950 1gb. fps benchmarks for 1 gb and 2gb 6950 are identical at res <2560x1600 (30-40usd less). If you're planning to CF in the future, IMO the 6950 1gb is the better card than the 5870. the 6000 series show a 15-20% boost in scaling from the 5000 series. tho nvidia is giving out crysis 2 with the 560ti...
these choices, building the pc is easy. choosing the parts is the hard part