Surely, the reason that Hawaii's power consumption might benefit more from aftermarket cooler is because like the classic IDC posts show, leakage at 95°C is a lot worse than at 83° or so where the reference GTX 780TI runs at. So yes, in theory both would probably benefit from aftermarket coolers but the 290X should get a bit more from it.
In theory that is: but as blackend23 pointed out, non-ref models tend to have fancier power delivery, run at different voltages and get to charge premium for being factory overclocked. Now in theory AIBs could bin parts for their OC's but most don't (still have a sore point with my Gigabyte Windforce 7950 forcing 1.25V mostly because Gigabyte can't be bothered to bin their chips - mine runs LTC fine at 1022/1500 with 0.95V for instance).
But anyway, 28nm TSMC is pretty much equal for GPUs isn't it? And once you take into account a few factors (GCN's higher DP performance vs GK104, die size of GK110 vs Hawaii) they two architectures have fairly similar perf/watt. Even the TPU chart shows a max of 70/100 spread which is hardly massive considering the chart has everything from 650/7770 to 290x/780Ti.
Still, since the temperature/leakage/power consumption thing should be very well known to anyone working in the industry, that makes AMD's decision to run with the old blower reference cooler even stupider (although I suspect a beancounter made the decision not an engineer).