Rabit has memory size modifying disabled for 1900XT/XTX bioses. I have talked to Rabit author, he said this function is experimental and it my not work at all. So he moddifed my bios for 1900Gt to 16/48, but it didn't work, I still got 12 pipes in Ati Tool and still same performance. Tried changing Device ID, still no go.
The only other way is to try to flash with 1900 AIW bios or if sb can modify 1900XT memory size to 256mb.