Wow you got 730KH/s out of the ASUS card without tweaking any settings? That's impressive!
I spent forever trying to get mine to push 700 and I've tweaked a bunch. It only ran at like 550-600 right out of the box. Do you know what settings it's currently running at to get that high?
Here is a screen-shot of my batch-file...

A pair of ASUS R9280X-DC2-3GD5 running an identical 735Kh/s... 1.470Mh/s average over the past 24 hours.