AMD has Bobcat APUs based on the 40nm manufacturing process technology, but it also offers some made on the 28nm process. The latter have been compared to the upcoming Kabini units.
Long story short, Kabini accelerated processing units will be around 10% faster than Bobcat. Some chips may even perform 15% better.
The fastest 40nm Bobcat processor, E2-1800, has a clock speed of 1.7 GHz and no Turbo Core.
28nm Bobcat units are even faster, and a Q&A video involving Jeff Rupley compares them to Kabini, not the others.
That would imply that Kabini chips work at more than 1.9 GHz. Add to that support for Turbo Core dynamic overclocking and there is even a chance for 2.4 GHz.
Either way, we still have to wait for the frequencies to become public knowledge.