I just got some info on BCLK ability of Gigabytes P55-boards. Using the GA-P55-UD5, an Core i5 750 cpu and some liquid nitrogen a BCLK of an astonishing frequency of 272 Mhz was seen. This means that even with the slowest stock cpu for LGA1156 probably won't be limited by the bus frequency.
http://elmor.se/img/news/750272bclk.jpg
Enjoy ;)