I don't have an answer for you, but I would also like to know why the i5-580M is rated at 4.8 GT/s. I have been digging all over to get an answer, and cannot find one. I find it hard to believe this could be a "typo" as some have suggested. Is there a way to benchmark and measure the GT/s rate empirically? Thanks
I stumbled upon the same lack of information, although I found a more extensive review on http://www.notebookcheck.net/Intel-Core-i5-580M-Notebook-Processor.33839.0.html . It does not answer the system bus question, but apparently they included it in their benchmarks, and it's doing surprisingly good. In some single threaded test it even surpasses the i7-920XM. I reckon we should just wait for the manufacturers to implement it in more notebooks, so there is a base for some more comprehensive testing.