well the extra 50watts would definately come in handy when doing cfx or sli setups as you really dont want to go for the bare minimum on power. however the antec 650w has 4 pci-e connectors which will be needed for the cfx/sli cards you mentioned or you can just use a 4pin molex to 6 pin pci-e adapter that comes with most GPU's and go with the 700watt Cooler master.
Plus that cooler master is modular which means you can only plug in the cables you need to use and keep the rest unattached from the PSU to reduce clutter of cable and improve airflow throughout your case.
IMO i would go for the cooler master, you never know when the extra 50watts will come in handy especially with crossfire as the last thing you want is for your system to run out of juice while your in the middle of a gaming session when you hit a GPU intensive part of the game and your system wants to draw more power but simply cannot.
with the 700watts you really cant go wrong, and plus its on sale for a really good price i see! thats really a steal at that price!
also both GPU setups you mentioned will be using up 450watts in dual card mode and thats only the cards alone which leaves you ~250 watts for the rest of your system if you get the 700w and ~200watts if you get the 650w so keep that in mind too