Haswell U-series w/ GT3, first detailed specifications
The speeds and feeds of two HSW ULT parts have appeared online.
Both chips are 2 core, 4 thread parts; have a 15 W TDP; and both feature HD 5000 graphics with a base clock of 200 MHz and a max boost clock of 1100MHz.
1.4 GHz base
2.9 GHz turbo
4 MB L3
1.7 GHz base
3.3 GHz turbo
3 MB L3
Unfortunately, the base clocks have taken a hit compared with IVB (between 300 and 500 MHz, depending on what you're comparing), though max Turbo Boost speeds have not. It will be interesting to see if parts without GT3 show the same decrease.
We'll have to wait for testing to see just how much performance you'll be sacrificing for the extra battery life that HSW offers.