Dunno if/when I'll see 5.1. I've just replaced my SGS3 with an SGS5 from Kogan, after the 3's USB connection got extremely flaky (I suspect a cracked PCB). Easy changeover, app-wise. Bit more than $150, Duncan. :)
It is dual SIM. -For when I travel to the next Ulysses AGM in Tasmania, where anything other than Telstra is next to useless. (When on a motorbike, one feels even more reliant on connectivity.) I'll get a Telstra prepaid for the second SIM slot.