What is the difference exactly between them?
The S3+ is overclockable so 50Ghash/s more?
They had an issue with the the DC/DC converter on some/most of the S3 (maybe a batch issue of that component or a just a flaw in their hardware schematic) Some units will run rock solid at 504 GH/s and others are not overclockable and run within 420-441 gh/s. I bought two S3 Batch 1. I got one very good machine and the other ... not so lucky. Having a hard time to make run to 441 (required many reboot) Sometime the magic happens and it runs at 441 for days but most of the time it is not. My second unit runs a rock solid 504 Gh/s forever.
They kind of fixed the issue with the S3+. I don't own an S3+ but they should be more overclockable.
The factory specs is
Hash Rate: 453 GH/s±5% with great OC potential for the S3+ versus
Hash Rate: 441 GH/s±5% for the S3.