According to HKEPC, who has compiled a list of the three upcoming Nehalem-based Bloomfield processors, the 2.66 and 2.93GHz non-XE versions will only get support for DDR3 memory at 1,066MHz, while the XE model clocked at 3.2GHz will have support for 1,333MHz DDR3 memory.
The XE model also has a faster QPI interface at 6.4GT/s while the non-XE models are stuck at 4.8GT/s, but this information is in itself not news, as this has been common knowledge for some time.
We're not sure why Intel decided to do this segmentation, although it's not the first time Intel has limited certain technology to a specific chipset or CPU. However, this time we expected the entire range to have nearly the same feature set, but it appears Intel had other plans.
We're not sure how much of a performance impact this will have, nor do we know if the higher speeds can be reached with some overclocking to the slower models. These are questions that we're sure will be answered in due time, but for now it looks like those that want that extra bit of expected performance have to save up some extra cash to get it.
More here (in Chinese).