The PSU in the RC-531 is a good PSU. It is not top of the line, but it is dependable and will operate at its rated capacities - something that a lot of generic PSUs can't accomplish.
You must have read the review from the one guy that had issues with the Asus A8N SLI Premium. The only "flange" that I could see from the pics that would have a
remote possibility of interfering with a connector going into the top slot was the angled portion of the back panel just below the 120mm fan. Look at this
pic. Even then I think it would take a large/cumbersome connector if that angle prevented the connectors installation.
That FSP is
really nice. You shouldn't have any issues with powering your system with that beast.
Interesting article about some 2 high-power PSUs, including the 700W version of yours. What video card will you be putting in your rig?