Common sense tells me that a dual rail system would be better since I've read that there is less chance of CPU RF interference unto other components when it is supplied power seperately.
My worry would be amperage load per rail on a dual 12V rail PSU,but since most dual 12V rail PSU's are newer I doubt you'd find one that underpowers your systems' needs if you aim for the 480+ watt PSU range.
It's more important to get a quality PSU from what I've read and understand.That means sticking with well known established brands i.e. Antec,Enermax,Fortron,PC Power&Cooling etc.
Personally I wouldn't lay too much emphasis on dual 12V rail when choosing.
Priorities should be 1.Quality PSU 2.True wattage(not just high advertised max. loads) 3.Cooling 4.Noise(dual fan vs single -80mm,120mm,140mm?) 5.Wire/Rail management (modular?sleeved?)
Dual 12V rail vs single rail falls in the priority category of unit color preference as far as I'm concerned.
The example you listed has sufficient O/P on the 12V rails for just about any desktop home computer you'd choose to slap together with high end components currently available.