The problem is that the OS will again be different. But that should be a more fair comparison.
I'd actually think if anything, Win RT would be more efficient because it doesn't need to support anything legacy.
If you want smartphones and modern SoC(Krait), its compared in the iPhone 5 review: http://www.anandtech.com/show/6330/the-iphone-5-review/12
That's about as close a comparison as you can get.
You can see that it has an advantage in the actual battery life test too, with the WiFi on.
That was interesting. And helps explain why Clovertrail has such a dramatic increase (over doubling) in battery life compared to the original Atom. It would have been interesting to be able to see the same comparison, except with an original Atom slate instead of Tegra 3.
Haswell ULV 10W is a CPU running at 1.1 GHz (turbo unknown) so it is not obvious it will be as power efficient as existing IVB 17W.
One of the biggest reason for Clover Trail doing so much better on the battery life department compared to previous generations is that the platform is capable of supporting Connected Standby, the Intel version being called S0iX.
While its to be seen how much Haswell improves at near-TDP levels, the ULT(Ultrabook-class) platform getting Connected Standby and S0iX support will help nicely in most other scenarios.