I wouldn't worry too much about rails, generally they come from the same primary source anyway. In this instance the total power for the 12v is 46A/552W, which is quite a lot.
You should be concerned about the combined 12v wattage.
[IM*]http://img189.imageshack.us/img189/2856/mxspwattagechartst.jpg[/IMG]
Its actually pretty poor for a 700w psu. As others have said, the hx620 from corsair has combined 12v output of 600w.