Those underpowered processors were only used as an optimization benchmark; if it runs good enough there, you could always throw more computational power and cores at it.
EDIT: Also, the numbers were in MiB/s (mebibytes per second), not Megabits per second; 10.5 MiB/s would be ~88 Mbp/s (megabits per second).
Again, I am under the impression that SYN flood is an essentially solved problem in the linux kernel and is defeated by the use of SYN cookies, which leaves the main DoS mechanism to be BW exhaustion... I'm pretty sure there are more effective ways to achieve this...
As for the question wtf is this useful for - debugging issues in your network. E.g. I recently used ping -f to track down an ethernet cable causing around 0.5% of package loss...
EDIT: Also, the numbers were in MiB/s (mebibytes per second), not Megabits per second; 10.5 MiB/s would be ~88 Mbp/s (megabits per second).