We're looking at Apple's documentation to see if the new Core i5 iMacs have a faster frontside bus than current iMacs. Apple's tech specs page is as ambiguous as possible just putting a placeholder where the speed should be under the Core i5 and not even listing any specs for the Core i7 model. Some Core i5 and i7 chips have 1333MHz bus speeds which would speed up the whole system significantly.
The speed bump would also increase the speed of the RAM however, which isn't indicated by the table.