Part of the Furniture
Broadcom supports CPU throttling/frequency scaling on the BCM4908. This could make a difference depending on whether or not this is enabled by either manufacturer. Personally I would prefer it to not do any scaling, since networking can be very latency-sensitive.
I have no problem with scaling....
$ sysctl dev.cpu.0.freq_levels dev.cpu.0.freq_levels: 2100/8 1800/0 1600/0 1400/0
I suspect that Broadcom has tuned the SDK appropriately