those are the things the seasonic does best but they dont indicate in any way whether its a good psu, its probably not hard (though ive never tried) to make a psu thats unstable and underpowered but nice and quiet and efficient
i know its not reliable at all as they would have been tested differently but i think they are fairly representative,
here the seasonic has dipped under 12V on both rails with 263W load and
here the st60f goes up to something like 550w load before it does that, and its still well within ATX spec under 662W load, which is pretty amazing for a "600W" psu
high output, low dipping and low ripple are the things that are going to keep your system stable and that puts silverstone and pcp&p and a few others in a different class, and it doesnt cost any extra