Transceivers in Cyclone IV GX

Hello everybody,

is there no way to drive the CycloneIV GX Transceiver Hardware with less 
than the 600MBit mentioned in the datasheet? I'd like to make use of the 
hw-ser/des and 8b10b-parts of Cyclone IV GX but didn't want do be faster 
than 100 - 150 MBit for multi-FPGA-Communication (because of topology 
reasons).

Thanks for answers.