Based upon the consumer reviews, I would stay away from that HEC psu. I don't know too much about them. I would go with a name brand - Corsair, PC Power & Supply or Cooler Master. Thermaltake and Antec are good too, but you'll spend a little more.
Keep in mind that those cards you picked out are all OC versions. A friend of mine picked up the MSI 260 OCv1 and he had a Logisys 650w psu and it would not support it.
They say a 750w should handle it. I myself have a 750w PCP&S psu running 2 4870s 1 GB which are near the same in performance as your cards. However, I would recommend going up to the 850w if you can afford. I know those MSI video cards are demanding power wise.
Here is mine:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817341011
http://www.newegg.com/Product/Product.aspx?Item=N82E16817703009
Note that is only has a single rail, as opposed to the HEC which has 4 rails, which may explain why some people are having problems with if they do not balance out the workload over all 4 rails.
I always prefer a single rail psu over multiples.
For the money, that Corsiar 850w is probably the best deal. Otherwise, sell your HEC, or go with 1 card, preferably a factory standard one, and then add a second if it works ok with one.