Ultimately tuning for best WU is the way to go as we don't get paid for the hash rate.  I'm finding that it's much easier (takes much less time) to adjust clocks and other settings when tuning for max has rate as the response is fast.  Tuning for max WU rate is slower as it's a long-term average.

Spend some time in CGMiner changing clocks 1 MHz up and down at a time.  I noticed trends up or down in some ranges, with spikes up or down 1 MHz farther.  It'll be worth your time to chart 20 MHz either side of your chosen frequencies (one at a time).  What you find will be 'normal' for your system - trust your findings.

I don't have enough experience yet with the R9 290, but spent some 'quality time' tuning four 7870s and those puppies just ain't normal.   Whoever wrote the BIOS for those was smoking something they really should have shared with the rest of us...