I would think that it will be good enough for many of them, but the PAR values will tell you exactly what you can successfully keep. The manufacturer's website recommends one 12K White & 1 Actinic for soft corals, so you could probably extrapolate that to what I mentioned.
IMO, if you don't mind buying twice, then just get another 12K White and see if you can keep an SPS frag alive then go from there; you can always buy the other 12K White later if it's needed. If it's not needed, then you can add another actinic strip to help improve the colors.
