The SP20 is equivalent to the S3 in all aspects.  I don't know why SPTech would release that unit, at that hashrate, at that delayed timeframe because it's no better than an S3 which is shipping today.  Waiting another 6 weeks for something I can get next week (new), or now (used)?  No thanks.

I'm going to assume the S4 will be better than the SP20, and arrive sooner.  It should follow the same upgrade path just like the S1 -> S3.  Meaning, it should just about double the hashrate for the same wattage, which will mean 2th/s at 1100w.  I see it coming in at around 2.2-2.4th/s at 1200w, but that's just my guess.  The only real question is the price.  If it's up around $1800 like the original was, it's a hard sell.  If it's down around $1400 or lower, then it's a good unit.  If it's around $1000, then back up the truck...