Looking at the following image:
Cisco is quoting the 7009 as having a 10GigE density of 336 and a backplane bandwidth of 550G/slot. The only way to get 550Gig/Slot is to have 5 FAB modules, taking up five slots. There is no possible way to get 336 10GigE (7 slot * 48 port/slot) since the switch must have FAB modules.
I am asking this because I am specing out switches and can not see the purpose of purchasing a 7009 since this switch takes double the RU and contains the same amount of IO slots as the 7004. It contains the same amount of IO slots as the 7004 because 5 of the 7 remaining IO slots must be used on FAB modules to get the same performance as the lower end 7004. The 7004 has built in FAB modules and also takes only two IO slots.