Why not just a lower-clocked OMAP4470? It looks like the performance that a ~300MHz SGX544 would have.
Or maybe a Nova A9540? Samsung has a couple of handsets using SoCs from ST-Ericsson (Galaxy Ace 2, Galaxy S Advance).
By the time you assume that it could be any other SoC not from Samsung with lower CPU or GPU frequencies than usual it sounds likelier that it's a lower clocked engineering sample than anything else. The Nova A9540 is supposed to have its 2*A9 at up to 1.85GHz if memory serves well and I'd be very surprised if they'd clock the 544 at only 300-350MHz; that under 32nm. Novathor L8580/28nm wil have its dual A9 clocked at up to 2.3GHz and the SGX544@600MHz.