CoreConnect Bus : How to speed up the PLB

Dear all, I am using Virtex-II Pro device and testing the data transfer rate between PPC and PLB-BRAM(or PLB-GPIO). All peripheral access functions are directly taken from Xilinx driver. Finally I found out that the maximum PPC to PLB-BRAM data transfer rate is only about 50Mbps!! This is far from the noted figure(hundreds of MBps). I would like to know how to speed up the data transfer rate in this case. Where can I find such information. I only found the 'burst' transfer feature available in PLB-BRAM datasheet,while don't know how to employ it in real C application. Thanks for your kind advice or discussion! Rgds, Jeffsen