I've the same card (omega). It's can go up to 1.45v if i remember because of the controller he have. Ocp mod didn't helped. Your frequency for that temperature seems low. At dice i can run it at 1720-1760 depends on the bench.

There supposedly is a edited firestorm software that is able to push 1.6v but I couldn’t get it to work. And frequency was that low because I ran really low on dice and wanted to get through some benches. Gpupi was good up to 1850 though.

You must the usb cable for the firestorm to go up to 1.6v if i remember well.