Uncompressed transfer rate is 'just' 250Mbps
It looks like IBM's assumed compression ratio is 2.6:1. The spec sheets on the IBM site describe the 'native sustained data rate (uncompressed)' as 250Mbps, putting it only slightly ahead of the T10000c. (source: http://public.dhe.ibm.com/common/ssi/ecm/en/tsd03127usen/TSD03127USEN.PDF)
It's still an impressive looking bit of kit though!