Details from the German site "ComputerBase".
Original and
Google translated.
Seymour Pro HD 7430M 600MHz 64bit / 900MHz ddr3
Seymour Pro HD 7450M 600MHz 64bit / 800MHz gddr5
Seymour XT HD 7450M 750MHz 64bit / 900MHz ddr3
Seymour XT HD 7470M 750MHz 64bit / 800MHz gddr5
Seymour XTX HD 7470M 800MHz 64bit / 900MHz ddr3
Seymour XTX HD 7490M 800MHz 64bit / 800MHz gddr5
Thames LE HD 7510M 450MHz 64bit / 800MHz 1GB ddr3
Thames LE HD 7610M 450MHz 128bit / 800MHz 1GB ddr3
Thames LP HD 7530M 450MHz 64bit / 900MHz 1GB ddr3
Thames LP HD 7550M 450MHz 64bit / 800MHz 1GB gddr5
Thames LP HD 7630M 450MHz 128bit / 900MHz 1GB ddr3
Thames LP HD 7650M 450MHz 128bit / 800MHz 1GB gddr5
Thames Pro HD 7570M 600MHz 128bit / 900MHz 1GB ddr3
Thames Pro HD 7590M 600MHz 128bit / 800MHz 1GB gddr5
Thames XT HD 7670M 600MHz 128bit / 900MHz 1GB ddr3
Thames XT HD 7690M 600MHz 128bit / 800MHz 1GB gddr5
Chelsea Pro (unknown) 450 - 550MHz 128bit / (unknown) 2GB gddr5
Chelsea XT (unknown) 600 - 700MHz 128bit 2GB gddr5
Heathrow Pro (unknown) 550 - 650MHz 128bit 2GB gddr5
Heathrow XT (unknown) 650 - 750MHz 128bit 2GB gddr5
Wimbledon Pro (unknown) 650 - 750MHz 256bit 2GB gddr5
Wimbledon XT (unknown) 700 - 750MHz 256bit 2 - 4GB gddr5
Should be interesting to see what performance difference there will be between DDR3 and GDDR5 cards.